Forgive me for such a long post. I currently use v1.3.9h and I paid a company to install the following add-ons to my store and now "admin settings" is showing the same error as the first post. Could any of these add-ons cause that problem? :

Categories Dressing
Better Together
Define Pages Generator
Group Pricing (per Item)
MCEditor
Admin Category / Product Images
Maximum Amount Allowed In Shopping Cart
Ultimate SEO URLs
Quick Updates
Search Log
Quickbooks Import QBI
AutoFacebook
AutoTweet
Social Bookmarking
Contest System
Google Analytics
Google Base (Froogle) Feeder
SitemapXML
Snap Affiliates
Google Checkout
Add Customers via Admin