Are you currently using Mozilla Firefox? I ask because recently, this changed to a 64bit only browser type, similar to what Google Chrome had done a few months ago. If so, you can use the steps below to work around this issue:
•In the address bar type: "about:config"
•A message will pop up for dangers of the these options agree to them.
•Search for "xpinstall.signatures.required". It should have a value of True.
•Right click on "xpinstall.signatures.required"
•"Toggle" the value will change to false.
Mozilla is currently working on a permanent fix, but this should work for you in the mean time. If you are not using Firefox, please let us know which browser you are using.
I hope this helps!!
Sling Media Technical Support