GGSN - Code 211 - All dynamic addresses are occupied

Hi Experts,
Any idea why there would be cause code 211 sent by GGSN IN create PDP response - ALL DYNAMIC ADDRESS ARE OCCUPIED?

IP Pool congestion.

This site can also be useful for GTP Cause Codes.

211 (GTPv1)
All dynamic PDP addresses are occupied
Indicates that the GSN does not have a free dynamic PDP address to allocate any longer.

Checked: IP Pool, DHCP, everything ok.
SGW reselection is not working when cause #84 received from ggsn.

Got this from a friend:
Each APN has IP pool for it inside GGSN.
For example IMS APN has 100 IPs.
If 100 IPs assigned, then new users will get error code 211.