Certain links redirect to errors?

Have you tried:

– deactivating all plugins to see if this resolves the problem. If this works, re-activate the plugins one by one until you find the problematic plugin(s).

– switching to the Twenty Eleven theme to rule out any theme-specific problems.

– resetting the plugins folder by FTP or PhpMyAdmin. Sometimes, an apparently inactive plugin can still cause problems.

Did you try any of the other suggestions I gave?

Try resetting your custom permalinks back to the default setting via Settings -> Permalinks and deleting (or re-naming) your WordPress .htaccess file. If this works, then review Using_Permalinks before setting a custom permalink structure back up again.

Then the re-direction is coming from something else on your domain/server.