I got the issue resolved. We were performing masking operation multiple times on a lun in a quick succession due to a repeated entry of a device in device list. It is resolved. Thank you for the reply.
Hello,  When I am trying to remove/add a volume to a Storage Group on VMAX I am getting following failure. Can some one let me know what is the issue here? I am using EMC ECOM to perform operations. I am not sure when this issue occurs. This is happening during both Masking and Unmasking of volume. Engnuity is VMAX20K   5876.  [(string)ErrorDescription := Masking group: Remove members - Device Masking Group at step Issuing StorDevGroupControl failed: C:ERROR_CLASS_SOFTWARE F:ERROR_FAMILY_FAILED R:1200034 L:2 C:ERROR_CLASS_SOFTWARE F:ERROR_FAMILY_FAILED R:1200034 Device not found in device group. : "StorDevGroupControl failed" : 2 : 28032 : "The specified device was not found" 
Getting error while masking/unmasking device on VMAX