Well, I started to use the email support and found out that Adabas must be installed in the "Adabas" folder directly on the C: drive, because it can only have 40 characters in the path description, and NO spaces!! XP naturally wants to install any program to C: Programs Files/ Adabas/.... So, the space in "Program Files" may be the issue. I uninstalled and reinstalled to C:/ Adabas and it opened OK.
But this is all a bit complicated for me, so I have started to look for a manual. I cannot seem to find one. I did find a download for Adabas 12.0 on the AGSoftware site, but it was in the *.tar format, which is not recognized by Microsoft, I mean XP. This could be of help to those with Linux. So, I am still looking for a manual download, a book, something...