Corel X7 - save and unable to close document - fix?

Hi there
Randomly, but more often that not, I can open a document, make changes, save the document, but then I cannot close the document without opening Task Manager and shutting down the whole application.
Despite further amendments the save button will not re-appear unshaded and the document will not close.
I've persevered for months hoping for an update that will fix this problem, but to no avail.
I cannot see anyone on the forums with a similar problem.
Using version 17.1.0.572 of CorelDRAW X7 on a Windows 8 PC.
Any assistance would be greatly appreciated.
Regards
Stuart Owen