Lock problem

Last weekend I needed to drop one index and add another on a table. We are a 24X7 shop, so I just wait until the wee hours of the morning and try to grab the table. It kept giving me a 'non-exclusive access' error. So... Instead of continuing to try to run the drop and create commands, I added a 'lock table xxx in exclusive mode;' line. I got the lock -- but then it still errored on the drop and create statements with the same non-exclusive error. I'm confused -- if I got an exclusive lock on the table -- why was it telling me I couldn't get exclusive access when I tried to do the index commands? We're running 7.22UC2 on an HP9000 - 10.20. Any insights would be appreciated. Tom Grenier DBA, Biztravel.com