HI!
I hope you have at least 2.5.2 version of Cqrlog in use.
Qso list loads max 500 qsos at a time. So you can not scroll (or delete) more in one go.
When you get to the edge press PgDN or PgUP (depending direction you are scrolling) to get more qsos loaded from database.

If Pg-keys do not solve this problem then look at the qso that is the last one you can see and from what there should be more qsos either to past or future time.
When you find the edge qso try to find same qso from ADIF file with text editor.
When found look at the next qso. (or few of them) There might be some kind of error in that (those) qso records.

Cut the qso record away from adif. statrs with <Call and ends to eor> Save file and try to import ADIF to new empty log.
I have once seen that kind of problem. There was one UTF8 special character in tag that was not "INTL" type.

If you can not find anything try to split ADIF file with text editor to around 8 chunks (abt 500 qsos per part).
Add empty line and then <EOH> to next line to start of every other partial file than the first one that already has ADIF header.
There is no need to have more than empty line and EOH to simulate ADFI header.
Then import partial files, one by one, and see when the scrolling stops. Then you know what part has error and it is
easier to pinpoint faulty qso record(s).