How UE capability enquiry procedure failure happens in LTE?

Question

why does MME need the "UE Radio Capability" information for an UE during attach procedure ?

Answer 1

As such , there is no failure message defined for UE Capability Procedure.
There could be one reason for that since this procedure is an enquiry procedure.
However, each procedure is associated with a maximum delay for its completeness.

Please refer "Processing delay requirements for RRC procedures" section in 36.331 spec to get the more details.