Regarding to the runtime error, please send more detailed information to DriveHQ customer support. Such problem is usually caused by anti-virus software / security software.
If you use DriveHQ Online Backup, try to create a smaller test backup task and see if it works fine. If you use DriveHQ EmailManager, please try to use the drag and drop feature instead of the automatic backup feature to pin-point which email has caused the software to crash.
Regarding to service cancelation, you can easily cancel your subscription online. Just go to the same Subcribe page and click on Current Subscription. DriveHQ requires the user to delete files and cancel subscription online.