Hi Christian,
Are you sure the password of sapsa is the correct one?
You may check by connecting to the system server as user "syb<SID>'", then run the isql command tool like this:
isql -S<SID> -Usapsa -P<your_password_here> -X
If you have "login failed" message there, that means the password is not correct, and if noone remember it you might need to reset. You can reset it by login into isql session as sapsso user and follow step 4 from Note 1706410 "SYB: Security - Changing passwords for database users"
If you don't know it either, you may follow instructions from Note 2008256 - How to reset master password for sapsso user and then step 4 of same Note 1706410.
Remember that after any password change, you have to change also on the secure storage, that is also mentioned on Note 1706410.
Regards,
Victoria.