Backup seems to be fail all the time due to 2 different reasons

Product: Acronis Backup & Recovery 10 (build 10.0.13762)

The backup seems to fail due to 2 errors (at separate times). The first one is the program cannot find the task ID. I know how to resolve it by removing the task script but it keeps occurring again, can anyone help me resolve this more permanently? the 2nd message i am getting is, cannot open "last_backups.xml". I have not found anything to deal with this error message yet. I am at the point of completely removing the software and reinstalling but would rather see if there was a resolution to the above first as that may not resolve it. thanks in advance.

Update 18/01/2012
I removed the software and reinstalled again. This seem to resolve the issue until the program encountered a problem (no backup drive in, disk full, etc). Now after encountering the problem of the disk drive being full, the program is very sporadic at working and not working fully. It will backup okay but hang at 100%. when i check the logs, it is cannot find task id error. This is the main cause of it sticking at 100%. I know how to remove the tasks that the program should delete but i really need a resolution to stop the program doing this. I cannot remove and reinstall on a regular basis as this is not practical. Does anyone have any ideas or any thoughts that i could be pointed in the right direction? many thanks.