An Oracle-BDE connection problem

My team has been working with Oracle8.0.3/NT and BDE5.01 for weeks.
When I wanted to install Oracle Client 8.1.5 on their PC,
everything worked fine during the installation, including the test
with Oracle Easy Config or SQL*Plus.

But... it doesn't work any more with the BDE.
When they try to connect with SQL Explorer to any DB (O8 or O8i),
they get the message :
"Invalid user/pwd - ORA-24324: service handle not initialized"
Any idea ?