I see labels like "common.cs.7" on my site instead of the usual text that would be displayed there.

This is caused by a string resource that is either not loaded, or missing.

First, just restart the site through IIS or by "touching" the web.config file.  The software will try to reload all of the strings upon restarting.  If the issue is not corrected, you may have to manually reload the strings.

To do this, make sure that the string file in the StringResources folder on your site is the correct file for the version of the software you are running (re-extract from the original .zip file if necessary).  Then go to Misc->String Resource Mgr and selecting the locale you are using from the Locale dropdown menu.  Click the "Reload from Excel file on server" button and run through the prompts to reload that string file.  Reset your cache, and the issue should be resolved.