Doug is absolutely on the correct track but didn't mention the 'MISSING' reference issue. I contacted Microsoft about this years ago and this problem is causing nightmares for people. They explained that when the application is being started it will try to identify all the libraries needed for the application. They do this by programmatically checking the references for the application. These references may not be correct for any number of reasons. Anyway, when they are not able to resolve a reference it is tagged as missing and the search for libraries is stopped. So all the references to libraries past any listed as 'missing' are unresolved and can't be used. Normally that ends up with Access showing code errors on standard Access type objects which have been used forever. The Database, Recordset, etc. Hope this helps.
If you receive an error such as "Undefined Function," "Function not available in query expressions," or you can't find the object or property you're looking for, then you probably lost some of your library references when you last upgraded. Fortunately, problems with missing references are easy to resolve. Simply open a module or the VB Editor and select References... from the Tool menu. Check the listing in the Available References control. If you find one tagged "Missing," uncheck it. Then, from the Debug menu choose Compile and Save All Modules or Compile VBAProject. Doing so should locate and reestablish your missing references.