Hi there,
Better late than never, I hope. I had exactly the same problem, which occurred because I resized the partition during Bitlocker decryption. I was also unable to resume decryption after successfully pausing using manage-bde.
The solution I found was to resize the partition back to what it was before I made the change using disk manager, and then to resume decryption using manage-bde -resume. It worked! Hopefully it will work for you too.