Andy Hush says:
I'm having the sample problem. Version 1.4.1 of the plug-in. A question mark is ...

I'm having the sample problem. Version 1.4.1 of the plug-in. A question mark is inserted as the first character of every AssemblyInfo.cs. msbuild fails with:

Properties\AssemblyInfo.cs(1,1): error CS0116: A namespace cannot directly contain members such as fields or methods

I think it's a real question mark, not a unicode indicator.

EDIT: Looking at the code, FilePath.readToString() and write() are used. According to the documentation, readToString() uses "current system encoding". For Windows, that is code page 932, aka windows-31j. However, my AssemblyInfo.cs files are UTF-8. I believe that Visual Studio uses UTF-8 by default. So perhaps the solution is to use core Java classes that can deal with different encodings. I am not a Java programmer, so I don't know what those would be.

Source : https://wiki.jenkins-ci.org/display/JENKINS/Change+Assembly+Version