Thank you for your post.
I am unable to replicate the problem. I created a RunTime solution using FileMaker Pro Advanced 10.0v3 under Mac OS X 10.6.6. I then created the same RunTime solution using FileMaker Pro Advanced 11.0v3 under Mac OS X 10.6.6, and the application successfully overwrote the previous RunTime folder. As you mentioned, all your other solutions overwrote the old solution properly.
Error 20412 usually refers to incomplete files being copied, so there may be something about your one solution FileMaker doesn't recognize. In any case, the removal of the old solution prior to creating the new solution appears to work. Let me know if you want me to pursue this further.
Thanks, TSGal, for attempting to reproduce this problem and for providing detail for Error 20412.
This problem has not recurred since my original post. Let's hope that continues.
I opened this thread (1) in case others encountered the problem and (2) to let the FileMaker team know it happened.