This "Wow, you exceeded the number of package names" error message happens because Cydia is currently based on a version of APT that can only support having 65k packages available from your installed sources.
You can fix the problem by removing some of your sources (by going to Manage -> Sources -> Edit on iPhone/iPod touch or to Sources -> Edit on iPad). That will put the number of available packages below 65k so that you can use Cydia again.
If some sources seem to not have a "remove" button when you try to remove them, that usually means they were installed as packages. Go to Manage -> Packages on iPhone/iPod touch (or to Installed on iPad), find the package with the source's name, and uninstall that package.
Keep in mind that pretty much the only way to get to this error message right now is to have several pirate repositories installed (since the default repositories only add up to 41k packages, and legitimate non-default repositories tend to be small). So, to work around this limitation, it's best to uninstall pirate repositories and keep legitimate ones. The default legitimate repositories are BigBoss, Cydia/Telesphoreo, Dev Team, ModMyi, and ZodTTD/MacCiti.
