This has been reported several times.
The Sophos program thinks that one of the data files contains a \"pinwheel\" virus, and deletes it. This casuses the program to crash, when it can\'t find the file.
It\'s a false positive, as the file in question is just a data file.
There two cures:
1) use a different virus checker
2) exclude the entire BOINC folder from checking.
Norton is another program that causes problems, but by locking files before checking them. When this \'locking\' co-incides with the program trying to access the file, it crashes. Same cure.