Unity 5.1.2 - previously could, but now unable to build to iOS

Question

I am creating a game using Unity 5.1.2.

Till last week I was able to build to iOS. But now suddenly, am getting lot of il2cpp related errors due to which I cannot build anymore.

Have tried opening old builds, installed Unity 5.1.2 p1.....but the same errors keep cropping up (in total four, mentioned below):

--- IL2CPP error (no further information about what managed code was being converted is available) Additional information: Build a development build for more information. Failed to resolve assembly: '.../v0.23 (On Sep 2, Version=0.0, Culture=neutral, PublicKeyToken=null'

--- Failed running /Applications/Unity 5.1.2 p1/Unity.app/Contents/Frameworks/il2cpp/build/il2cpp.exe --copy-level=None --emit-null-checks --enable-array-bounds-check --extra-types.file="/Applications/Unity 5.1.2 p1/Unity.app/Contents/Frameworks/il2cpp/il2cpp_default_extra_types.txt" --assembly=".../v0.23 (...)/.../Temp/StagingArea/Data/Managed/Assembly-CSharp.dll" --assembly=".../Temp/StagingArea/Data/Managed/UnityEngine.UI.dll" --assembly=".../Temp/StagingArea/Data/Managed/UnityEngine.dll" --generatedcppdir=".../Temp/il2cppOutput/il2cppOutput" --builder=none

stdout: IL2CPP error (no further information about what managed code was being converted is available) Additional information: Build a development build for more information. Failed to resolve assembly: '.../v0.23 (On Sep 2, Version=0.0, Culture=neutral, PublicKeyToken=null' il2cpp.exe didn't catch exception: Mono.Cecil.AssemblyResolutionException: Failed to resolve assembly: '.../v0.23 (On Sep 2, Version=0.0, Culture=neutral, PublicKeyToken=null' at Unity.IL2CPP.Common.AssemblyLoader.Resolve (IMetadataScope scope) [0x00000] in :0 at Unity.IL2CPP.Common.AssemblyLoader.Load (System.String name) [0x00000] in :0 at Unity.IL2CPP.AssemblyConverter+c__AnonStorey1.<>m__0 (System.String path) [0x00000] in :0 at System.Linq.Enumerable+c__Iterator102[System.String,Mono.Cecil.AssemblyDefinition].MoveNext () [0x00000] in <filename unknown>:0 at System.Linq.Enumerable.ToArray[AssemblyDefinition] (IEnumerable1 source) [0x00000] in :0 at Unity.IL2CPP.AssemblyConverter.Apply () [0x00000] in :0 at Unity.IL2CPP.AssemblyConverter.ConvertAssemblies (System.String[] assemblies, NiceIO.NPath outputDir, System.Collections.Generic.List`1 additionalCpp) [0x00000] in :0 stderr:

Unhandled Exception: Mono.Cecil.AssemblyResolutionException: Failed to resolve assembly: '.../v0.23 (On Sep 2, Version=0.0, Culture=neutral, PublicKeyToken=null' at Unity.IL2CPP.Common.AssemblyLoader.Resolve (IMetadataScope scope) [0x00000] in :0 at Unity.IL2CPP.Common.AssemblyLoader.Load (System.String name) [0x00000] in :0 at Unity.IL2CPP.AssemblyConverter+c__AnonStorey1.<>m__0 (System.String path) [0x00000] in :0 at System.Linq.Enumerable+c__Iterator102[System.String,Mono.Cecil.AssemblyDefinition].MoveNext () [0x00000] in <filename unknown>:0 at System.Linq.Enumerable.ToArray[AssemblyDefinition] (IEnumerable1 source) [0x00000] in :0 at Unity.IL2CPP.AssemblyConverter.Apply () [0x00000] in :0 at Unity.IL2CPP.AssemblyConverter.ConvertAssemblies (System.String[] assemblies, NiceIO.NPath outputDir, System.Collections.Generic.List1 additionalCpp) [0x00000] in <filename unknown>:0 [ERROR] FATAL UNHANDLED EXCEPTION: Mono.Cecil.AssemblyResolutionException: Failed to resolve assembly: '.../v0.23 (On Sep 2, Version=0.0, Culture=neutral, PublicKeyToken=null' at Unity.IL2CPP.Common.AssemblyLoader.Resolve (IMetadataScope scope) [0x00000] in <filename unknown>:0 at Unity.IL2CPP.Common.AssemblyLoader.Load (System.String name) [0x00000] in <filename unknown>:0 at Unity.IL2CPP.AssemblyConverter+<Apply>c__AnonStorey1.<>m__0 (System.String path) [0x00000] in <filename unknown>:0 at System.Linq.Enumerable+<CreateSelectIterator>c__Iterator102[System.String,Mono.Cecil.AssemblyDefinition].MoveNext () [0x00000] in :0 at System.Linq.Enumerable.ToArray[AssemblyDefinition] (IEnumerable1 source) [0x00000] in <filename unknown>:0 at Unity.IL2CPP.AssemblyConverter.Apply () [0x00000] in <filename unknown>:0 at Unity.IL2CPP.AssemblyConverter.ConvertAssemblies (System.String[] assemblies, NiceIO.NPath outputDir, System.Collections.Generic.List1 additionalCpp) [0x00000] in :0

UnityEngine.Debug:LogError(Object) UnityEditorInternal.Runner:RunManagedProgram(String, String, String, CompilerOutputParserBase) (at /Users/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:66) UnityEditorInternal.IL2CPPBuilder:ConvertPlayerDlltoCpp(ICollection1, String, String) (at /Users/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:402) UnityEditorInternal.IL2CPPBuilder:Run() (at /Users/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:293) UnityEditorInternal.IL2CPPUtils:RunIl2Cpp(String, String, IIl2CppPlatformProvider, Action1, RuntimeClassRegistry) (at /Users/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:211) UnityEditor.HostView:OnGUI()

--- Exception: /Applications/Unity 5.1.2 p1/Unity.app/Contents/Frameworks/il2cpp/build/il2cpp.exe did not run properly! UnityEditorInternal.Runner.RunManagedProgram (System.String exe, System.String args, System.String workingDirectory, UnityEditor.Scripting.Compilers.CompilerOutputParserBase parser) (at /Users/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:68) UnityEditorInternal.IL2CPPBuilder.ConvertPlayerDlltoCpp (ICollection1 userAssemblies, System.String outputDirectory, System.String workingDirectory) (at /Users/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:402) UnityEditorInternal.IL2CPPBuilder.Run () (at /Users/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:293) UnityEditorInternal.IL2CPPUtils.RunIl2Cpp (System.String tempFolder, System.String stagingAreaData, IIl2CppPlatformProvider platformProvider, System.Action1 modifyOutputBeforeCompile, UnityEditor.RuntimeClassRegistry runtimeClassRegistry) (at /Users/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:211) UnityEditor.iOS.PostProcessiPhonePlayer.PostProcess (UnityEditor.iOS.iOSBuildPostprocessor pp, BuildTarget target, System.String stagingAreaData, System.String stagingArea, System.String stagingAreaDataManaged, System.String playerPackage, System.String installPath, System.String companyName, System.String productName, BuildOptions options, UnityEditor.RuntimeClassRegistry usedClassRegistry) UnityEditor.iOS.iOSBuildPostprocessor.PostProcess (BuildPostProcessArgs args) UnityEditor.PostprocessBuildPlayer.Postprocess (BuildTarget target, System.String installPath, System.String companyName, System.String productName, Int32 width, Int32 height, System.String downloadWebplayerUrl, System.String manualDownloadWebplayerUrl, BuildOptions options, UnityEditor.RuntimeClassRegistry usedClassRegistry) (at /Users/builduser/buildslave/unity/build/Editor/Mono/BuildPipeline/PostprocessBuildPlayer.cs:316) UnityEditor.HostView:OnGUI()

--- Error building Player: Exception: /Applications/Unity 5.1.2 p1/Unity.app/Contents/Frameworks/il2cpp/build/il2cpp.exe did not run properly!

Have tried lot of solutions on StackO as well as the net, but no solution so far. Would really appreciate any help out there!

Kind Regards