You’ll have to dig out any references to the wrong version number. First, do as Marc says: get rid of all compiled assemblies that Visual Studio may be using. Also make sure that VS can’t find the wrong version in the GAC because it might be grabbing that one as well. Restarting VS is also a good idea as it sometimes retains caches references in memory.
If none of that works, then you have an explicit reference to the assembly using the old version number somewhere in your solution. Check project files for references with that version number; check those pesky
license.licx files (you can just delete the offending line from those).
Good luck! And be reassured, there’s always some logical reason for the assembly mismatch. It’s just sometimes tedious to find.