I have had issues in the past with an error exporting the ALE to Excel. It was always bothersome as I couldn't replicate it. Never bothered calling Sage for the ""yes, we charged you a case, but we don't have a clue"" response. Then one day I noticed that I had modified the ALE after it returned data (usually just by resorting a column), I got the error. If I didn't modify the lookup, it exported.
Have them try exporting the ALE IMMEDIATELY after it returns data. Don't touch anything in the lookup! Just export it to Excel.