can't stop unworking image job

Windows 8.1, Acronis True Image 2015, Build 6525.

The program starts a job looking for an external drive on a drive letter that does not contain the external drive I am using. Clicking stop does not stop the job, ever. It just keeps running "calculating time remaining."

I created a new job, but the program won't run it until the old job stops or finishes, which never happens.

I tried to change the drive letter of the external drive to the letter the program is looking for, but that letter is not available for assignment. It appears to be reserved under a grayed-out drive letter to a multi-card reader in the computer.

Advice please!

Thanks.