One Client Hang-ups......

We developed supposed to be a multi-user program...using Delphi 5 and
Interbase 5.6. however when  we try to connect with two user
simultaneously....or maybe with a little difference in access time.....the
second user hangs-up in the middle of opening the program.... and the first
one goes on.....i mean can run/use the program....

Is there something wrong with InterBase?

Please Guide us....

thank you...