I've been getting errors like
General error: Can't create/write to file,
Error 2006: MySQL server has gone away, and other similar PDOExceptions and errors from time to time while developing on my Mac using MAMP Pro (this seems to happen more often with Drupal 7 sites than Drupal 6, for reasons I know not). I've noticed a few other developers are getting these errors too, and almost always on local environments as opposed to live servers.
I found that the easiest way to deal with them is by giving MySQL a nice buffer of memory via the
innodb_buffer_pool_size settings. Just bump those up to 256M or higher, and the errors above should go away. (In MAMP Pro, just go to File > Edit Templates > my.cnf, and search for those variables. Uncomment the innodb_buffer_pool_size variable if it's commented out.
Typically this only happens if you're working with rather large databases, or if you're doing things like clearing all caches with a low max_allowed_packet size. Some people drop the entire database and reimport, but that seems like overkill to me—especially since I can always throw more RAM at a problem!
Further reading: MySQL has gone away [MySQL Reference Manual]