Cannot open the disk ‘D:\ubuntu\Ubuntu 64-bit.vmdk’ or one of the snapshot disks it depends on.

All you have to do is to delete the .lck file from the folder of your vmdk files. It is generally present at C:\Users\UserName\Documents\Virtual Machines\VMWareName

Also you can just move the lck files one folder up to ensure you do not delete any other file by mistake.