Yes 2.1. So far I have not seen it in 2.2. 
Weird
From
v2.1 to
v2.2 I have changed these 3 things:
1.- I have used the cache functions so now if you have cache enabled in your forum, everytime the mod do a dnslookup of an IP, it store the data in the cache for 120 seconds. This will make pages with lots of visitors load faster, but it won't affect at all to normal sites. And of course it won't affect you if you haven't cache enabled.
2.- In version
v2.1 I was using plain Mysql to display the page warning.php instead of the SMF functions db_query() or $smcFunc['db_query'] and I had put some default values just in case something went wrong. So the people using SqlLite or PostgreSQL were seeing in their warning.php always the default values.
I have found a way to sort that in
v2.2 so everybody now should see in the page warning.php the values they put in the settings and not the default ones. By the way, everybody should edit the file
httpBL_Subs.php to change my default values for theirs, just in case something goes wrong anyway with the db, but it's not too important. I will explain that better for normal users when I have time to continue the tutorial, so that can wait for now. (Advanced users can do it now).
Anyway this change (even if you are not using Mysql) only affects to the page warning.php, so I don't think it has anything to do with your error 500 either.
3.- In version
v2.1 I was using only $_SERVER['REMOTE_ADDR'] to find out the visitor's IP so we can check it out in the spammers db. Version
v2.2 is using a lot more methods. See full list here:
http://www.snoopyvirtualstudio.com/trankos/portal/index.php?option=com_smf&Itemid=36&topic=309.msg1292#msg1292I don't think this change can have anything to do also with error 500
Of course the problem is error 500 is too generic. It can be almost anything.
Any of the 3 changes were affecting you?
Was there any more information with the error 500? Normally no, so I suppose we will need to wait to see if it comes back again.
Cheers.