error E_FAIL

Hello,
I am using:
Delphi5
SQL Server 2000 or 7
MDAC 2.61

When I am trying to get data from server using ADO, I get error

'The data provider or other service returned an E_FAIL status'

The actual query selects 63 fields and has 29 LEFT OUTER JOIN's. Query which
has 62 fields, 28 joins and one EXISTS(SELECT.... ) less, runs fine.

What can be causing this? This happens only on one computer where SQL Server
7 is used, but not on others (server 2000 or 7).

Thank you.