Thanks for your tips, even if they didn't help this time.
i investigated a little further. So, db2cmd can be opened without any errors. Issuing any command like "db2 connect to ......" results in just returning the prompt without any output. what we found out is, that the errorlevel jumps from 0 to 8 after issuing any command.
DB2tempdir is set to "c:\program files\sqllib" where the user has fullcontrol.and where db2clp.dat resides.
Any other ideas, where to get more infos???
Client - db2diag.log reports this:
2006-01-19-16.34.08.583000 Instance

B2 Node:000
PID:3424(java.exe) TID:3532 Appid:AC11820E.890F.060119153134
base_sys_utilities sqle_db2ra_ar_rstdet Probe:18
DIA9999E An internal error occurred. Report the following error code : "0x
36".