Cause:

CellCLI> create griddisk MGMT_CD_cell12_stocell celldisk=CD_cell18_stocell,size=976M

CELL-02559: There is a communication error between MS and CELLSRV.

Workaround:

Check if all the three cell services (cellsrv,MS and RS)are up and running

CellCLI> list cell detail
.
.
.
         cellsrvStatus:          running
         msStatus:               running
         rsStatus:               running

If any service state is not running, then start the services

[root@exceladm00 raw]# service celld restart

Stopping the RS, CELLSRV, and MS services...
The SHUTDOWN of services was successful.
Starting the RS, CELLSRV, and MS services...
Getting the state of RS services...  running
Starting CELLSRV services...
The STARTUP of CELLSRV services was successful.
Starting MS services...
The STARTUP of MS services was successful.

After starting the services,you can continue your operations

CellCLI> create celldisk all
CellDisk CD_cell18_stocell successfully created

CellCLI> create griddisk MGMT_CD_cell12_stocell celldisk=CD_cell18_stocell,size=976M
GridDisk MGMT_CD_cell12_stocell successfully created