It sounds like one or more resource files is out-of-date or corrupted. You can try and update your Web Application's resource files with STSADM like so...
stsadm -o copyappbincontent
This command should update your Web Application's resource file. However, this command doesn't always work, especially when your IIS virtual directories reside outside of the INETPUB/WSS directory. If this doesn't work you can try an manually copy the file into your Web Application's directory. To do this simply copy the file..
C:\Program Files\Common Files\microsoft shared\Web Server Extensions\12\CONFIG\Resources\prov.resx
to
{Your IIS Virtual Directory}\App_GlobalResources\
Finally, your site may be looking for a local specific resource file like prov.en-US.resx. If you see a file like this in the App_GlobalResources directory please remove it. Perform an IISRESET to update your changes.
If this does not correct your issue please send a message to softwaresupport@sharepointsolutions.com and we'll arrange to have an system engineer look at your issue.