Reset IIS on the REWS or restart the REWS  The website is still looking for the previous Raiser's Edge files.  An IIS reset is good step to do after all upgrades.

To access the testconfig page:
If NetCommunity is on version 7.0 and below, review [netcommunityURL]/testconfig.aspx. 
If NetCommunity is on version 7.1 and above, refer to Access is denied warning when trying to view testconfig.aspx