I presume you upgraded to the different directory and copied original config files. For some reason your temporary files are in Config directory and were copied, too. In this case the error is probably benign and should be easy to fix. Just go to the c:\Program Files\Multiedit 9.10\Config\ directory and delete all BscRes*.TMP files. You may also want to delete all *.*_BSC_TMP files which could cause the same problem.
Before deletion, you can examine the first line of BscRes7.TMP file which should contain string WINFILENAME=<path>\BscRes7.TMP. If <path> points to your original Mew 9.0e directory, that’s what causes error messages. BSC signs its files this way and checks if there is an expected signature. Originally, it was for debugging purposes and I left it there just for paranoid reasons (so BSC can’t mistakenly rewrite a file which doesn’t own). It is probably supefluous checking.