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.