I ran into the same issue by copying a 'newer' copy of cci_debugger_plugin.dll into the load runner directory while trying to fix a different issue with .Net.
Now none of my scripts will complile and I get the error.
Timestamp of all the dll in the LR Directory are from the 4/23/2013 date. The newer copy of the debugger plugin dll file was 9/13/2013.
I'm sure that if I get the file back everything will work.