I have never installed mij B4A and B4J IDEs on the C drive and this is never a problem. The only problem is that some programs assume by default that you don't distinguish between standard Windows OS location and your data with additional software on a "data" disk. The key is to see if only this or that all programs have a problem. You will probably have another program to see if it can compile without errors. If so, chances are you are either using the already reported obsolete or wrong library, or you have a wrong hard coded reference to the program disk in your program or initialization (files) and you may run into a 32 or 64 bit reference and use of to other libraries versions.