If the backup client freezes or crashes, and you are unable to close it, then you may need to delete the running/stopped files created by the backup.

You will need to go to the user folder that the client was installed on, in this example I am using the Admin logon. Once there, you will need to open either the .obm (Business User) folder or the .acb (Single User) folder. Once inside this folder, open the .ipc folder, then BackupSet folder. In here there will be files that correspond to your backup set, they will however not have the names of your sets, but be names are after the set ID the software gives itself, this can be found on the portal under "Edit" in the "General" tab - or you can check all the files if you wish. In here there may be running or stopped files:

An example of this is below: