Can't locate loadable object for module main in @INC
@INC is set up correctly, in order to find the path in which
MyHandler::ModPerl20 is installed (I think what happens is that when Apache recycles some child, the one starting fresh do not have the correct
@INC value, hence not finding your module anymore).
Try to add a
PerlSwitches -I/your/path/for/myhandler/ in httpd.conf to see if it fixes your problem.
If that changes things, have a look at Adjusting @INC in modperl documentation to see all details.