Finally i could find the error by myself following these steps:
http://www.vbforums.com/showthread.php?348106-RESOLVED-HTTP-1-1-503-Service-Unavailable
https://support.microsoft.com/en-us/help/894435/how-to-switch-between-the-32-bit-versions-of-asp-net-1-1-and-the-64-bi
ASP.NET 1.1, 32-bit version
To run the 32-bit version of ASP.NET 1.1, follow these steps:
1. Click Start, click Run, type cmd, and then click OK.
Type the following command to enable the 32-bit mode:
cscript %SYSTEMDRIVE%\inetpub\adminscripts\adsutil.vbs SET W3SVC/AppPools/Enable32bitAppOnWin64 1
Type the following command to install the version of ASP.NET 1.1 and to install the script maps at the IIS root and under:
%SYSTEMROOT%\Microsoft.NET\Framework\v1.1.4322\aspnet_regiis.exe -i
Make sure that the status of ASP.NET version 1.1.4322 is set to Allowed in the Web service extension list in Internet Information Services Manager.
For beginners.. %SYSTEMROOT% is the Windows directory... in my case C:WINDOWS
Now this initially did nothing for me... so i navigated to the link in windows explorer, found adsutil.vbs and double clicked. It then asked me if i wanted to enable cscript (or something like that - can't remember cos i clicked too fast). Once i double clicked a second time all went well.
My Visual Studio was working again