Cannot save any modules
If you are getting that error is because you are probably using a shared host instance at 1and1, and these instances are mostly better for simple static HTML sites of the kind you would create by hand in Dreamwweaver, for example.

If you are hosting a small Drupal site with a few modules, a small database, and a few visitors, then perhaps 1and1's cheapest (shared host) package will suffice. But as your sites grow bigger, shared host packages tend to not cut it (regardless if they are hosted at 1and1, godaddy, dreamhost, etc).