IDMS DC016100 64-bit storage obtain

Document ID : KB000098015
Last Modified Date : 25/05/2018
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I'm having this message in one of my IDMS system migrated from 16 to 18.5 in testing. : 

IDMS DC016100 64-bit storage obtain (segments=0x0000000000000002) 
failed. R15=0000000C, R0=00002100 

What do I have to check on my idms to see why is trying to use extended addressing ?
This is usually caused when the CV's DMCL specifies the use of MEMORY CACHE for one or more files. MEMORY CACHE replaced DATASPACE specification as of 16.0. 
By default, IDMS will try to allocate the file in a 64-bit Memory Cache. If this 
fails we will try to allocate a Dataspace. If that fails the file doesn't 
get cached. 
Either you don't have 64-bit memory available at all or it is limited by 
the opsys parameter MEMLIMIT, so that the file(s) accessed by the jobs in 
question cannot cache the file in 64-bit memory. 
You can see this if you run an IDMSLOOK on the DMCL.