sy,
This could be related to a lot of issues. We see this most when customers are trying to image SSD drives. If you have not added the -NOTRIM switch then it may be trying to trim the drive (If it is SSD).
This situation has a variety of causes, no one solution will work in every case. Try each of the solutions mentioned on following link.
https://support.symantec.com/en_US/article.TECH106950.html