Boot Failure

The boot-up process for three PCs on a network is failing. Either they hang while the users are logging on or they simply crash.
When I switch them on again AUTOCHK runs and reports the error:
COMPAQ\WBEM\cache\USER0000\PORT08FD\cpqhsrf.frm first allocation unit is invalid, entry truncated
Still the PCs fail to boot and on successive restarts now the error becomes:
Unrecoverable error in directory Compaq\WBEM\cache\…

Question:
What does this error mean and how do I solve it?