Can't run a scan that used to be no problem

IQfeed version, Amibroker 6.39.1
I tried to run a simple scan and encountered the following problem. Any solutions?

Ok, I changed database setting "number of bars" from 2000 to 20,000 and it runs fine. The program I tried to run is to backfill about 900 symbols. I guess if the "number of bars" is too small, the program runs too fast that IQFeed can't handle. Am I correct? The thing is I don't need so many bars. Is there any other way to solve the problem? Thanks.

2000 bars is too small amount especially if you are using "mixed intraday/eod mode" as plugin tries to download at least 10 years of EOD data which is easily more than 2600 bars.
If you don't need EOD data, you can turn "mixed intraday/eod mode" off.

Apparently, the problem appears randomly. I successfully run the scan yesterday but not today. It has nothing to do with "number of bars". What's the meaning of those error messages? What caused Amibroker to crash?