blockUI - the unBlock does not work

blockUI - the unBlock does not work

I am using the BlockUI plugin with both Chrome 34.0.1847.116 and IE 10.0.14. 
 
$.unblockUI();
 
 does not work  - even as a test if I call it directly after
 
$.blockUI();
 (which works fine.)
 
Is anyone else having this difficulty and were you able to resolve it?
Thank you.
 
Kerri