Just to make sure there is no confusion, are C and D separate physical drives inside the computer?

If D is a separate drive, is it already partitioned into more than one partition? If so, what is on all the partitions? If there is only one partition are you attempting to create a new partition?

If that separate D drive is empty, does Easeus Partition Manager allow you to delete all partitions, and reformat?

What about using Windows own Disk Management console?

Not an expert myself, but the more information may be useful to others.

Mark