MME Initiated UE Context release Due to Transport Resource Unavailable

Question

I am facing the problem during UE attach

1. S1AP/NAS-EPS 134 id-initialUEMessage, Attach request, PDN connectivity request
2. S1AP/NAS-EPS 138 SACK id-downlinkNASTransport, Authentication request
3. S1AP/NAS-EPS 138 SACK id-uplinkNASTransport, Authentication response
4. S1AP 98 SACK id-UEContextRelease, UEContextReleaseCommand [Transport-cause=transport-resource-unavailable]

What is the reason for UE Context release

Comments

This means that "The required transport resources are not available" but cant say anything without much information on the case.
Can you please provide more details?