One of the components making up the signature of the VMFS has changed. Most often this is caused by a VMFS being presented on a different SCSI ID. This condition has also sometimes been caused by certain Dell PERC firmware upgrades and can be caused by major RAID failures (such as re-tagging drives after a multi-disk failure, etc.)
As with all good troubleshooting, you need to understand the situation before taking any action. Incorrectly jumping to conclusions on how to troubleshoot this could possibly lead to unnecessary data loss or downtime.
There is a VMFS Volume Management guide and numerous VMware KB articles that discuss the possible scenarios. It is important to read and understand all possible scenarios before taking action.
Read and understand the VMware VMFS Volume Management document before making any changes, as data loss can occur with certain configurations.
Generally speaking with a snapshot - the right behavior, is that you enable resignaturing, and rescan, and the LUN appears. With a DR cluster that hasn't seen that LUN before, you Disallow snapshot LUNs, rescan.
Note: **Before making any changes in production environments, it is ways a great idea to perform test on non-critical data in your own test environment, just like you do for your other mission-critical IT elements.**
Below is a list of good general-purpose troubleshooting KB's: