ODBC-Call for <DB-Name> failed

Hello all, 

is there any limitation how many simultanous sessions a single user can open
and how can I change this (I didn't find a possibility to change)?

I'm asking this, because I've been run into the same error a lot of times in
different circumstances. I'm using Access 97 as frontend and if I open for
example two objects (one connection and one database object) I get the error
'the ODBC-Call for <MyDB> failed'. I'm also running into the same problem if
I open a bound form (the tables are linked) which has one/some unbound
combo-boxe(s) which are filled through SQL-statements. Or I have open a
bound form and I try to open a linked table. Or if I tried to export 2
Access tables to SAP-DB it always failed on the second table. I had to close
and reopen my database for every table I wanted to export.
I forgot to mention, before I get the ODBC-Call error, the ODBC-driver Input
form pops up. 

I think it's SAPDB related, since I can't open a SQL-Studio-Session, if I
have Access open and the tables linked.

Regards
Peter