The message was created by fix NZ05521. This APAR adds warning messages when the NMSSI data space is running low on free space. It is normal for PDYNDBSIZE utilization to increase and decrease through out the day.
The default value for PDYNDBSIZE is 64. This can be increased to values of either 128, 256, or 512. The syntax for this PDYNDBSIZE=<value>. The parameter is set in the SSIPRM. You will need to recycle the SSI after the parameter is increased.