Delta was initially pleased with the A310 and found it efficient on the JFK-WAW routes and other routes to eastern Europe and Scandinavia. Regarding FLY777UAL's theory that subsequent A310 orders were made to appease the EU, the Treaty of Maastricht which created the EU from the EEC wasn't signed until summer 1991; when DL ordered the (very small number of) A310s from Airbus circa 1993-4, the EU wasn't a formidable economic force.
All that aside, Pan Am's A310s were in horrible condition - I know this from a first-hand source - and the Atlanta Journal-Constitution ran several articles on DL's financial stresses when DL was trying to integrate the Pan Am North Atlantic routes. The A310s were acquired from Pan Am to fill a niche, and when the market expanded, DL ordered just a few more. The aircraft, however, were acquired on short-term leases and the lease contracts were cancelled when it became difficult to: a.) integrate new aircraft (new Airbuses) with older aircraft that had not been well maintained (the Pan Am Airbuses); b.) integrate an Airbus fleet with a predominantly 767ER fleet and an L-1011 fleet, all operating in DL's Atlantic/European division from JFK and ATL; c.) economically operate such a mixed fleet to some of the same markets. DL found it more advantageous simply to acquire more 767s and not have an Airbus fleet in the middle of Boeings and Lockheeds, an Airbus fleet that was split anyway between new aircraft and Pan Am's aircraft, which had minor differences.
Additionally, the eastern European markets eventually became impractical upon the advent of the codeshare; one can imagine how low load factors were from ATL to, say, Budapest during the mid-1990s anyway. When it became more practical for DL to codeshare its European flights to LH at first, then SR and Malév, there was no need to continue the eastern European services and the Airbuses were no longer needed. Some went to Aerolineas Argentinas, in fact.
Summarily, yes, Delta did not like the Airbus fleet, not because of an innate problem with the aircraft or its design, but rather because of the problems of fleet integration and the fact that the Pan Am A310s were in horrible condition, not having been meticulously maintained during Pan Am's economic crisis and financial woes. Also, the mid-1990s were a bad time for Delta and the airline needed all the efficiency savings it could get during that time.
Hope this helps clarify some points made in this thread already and alleviate some confusion.