I would hazard a guess that you now have more than 8 megs of Fast Ram.
You can only have 7.5 megs of Fast ram and 1 meg of Chip RAM. What
has happened is that you have run out of AutoConfig Space. I had the
same problem when I added a 2620. I had to pull my 2 meg 2052. I now
have 8 megs of Fast RAM, and everything works fine.