1) Domain application pool fails with error:
A process serving application pool 'domain.tld(domain)(2.0)(pool)' terminated unexpectedly. The process id was '21412'. The process exit code was '0xffffffff'.
2) Crash report shows the error like below:
Unfortunately, this error doesn’t really give any useful information. Such issue should be investigated with Debug Diagnostic Tool. Often such issue indicate about PHP fault. See also PHP bug .
Try to switch PHP in domain settings to higher version (if domain uses old PHP version). For example PHP5.3 and check how domain works.