According to the error TF42097: A work item could not be saved due to a filed error.
The build uses the Default Template (or a customization) and has the Create Work Item on Failure option turned on, however the Bug work item has been modified in a way that means the build is unable to create it – which could be as simple as making a field mandatory.
How you fix this depends on how the Bug work item has been restricted. Work item fields that have been made mandatory should have a value specified in the build process template, and if that value should vary depending on the build definition you will need to expose it as an argument in the definition.
A workaround for this situation:
Adding in a PropertyGroup <SkipWorkItemCreation>true</SkipWorkItemCreation>
will stop it from attempting to create the work item.
A similar question from MSDN for you reference.