Hi I made sure that my project .pch file was gone and tried again without success. However there is a second project in the solution (on which my project is dependent). When I made sure the second project's .pch file was deleted it solved the issue. So your suggestion was spot on - thanks :) Now all I have to do is go through and correct all of the 'real' errors caused by previous developers not using the transmutable macros etc :( Thanks again.