I ran into every problem mentioned here in this forum. Found out that having newer and/or previous versions of Roxio Easy Media Creator and the associated registry keys still on my PC is what screws things up. Roxio/Sonic leaves a very big footprint on your PC. The "certificate is missing or file has been corrupted" message kept appearing until I followed Roxio's clean install instructions to the letter. Here is a link to the procedure direct from Roxio which worked like a charm for me.
Hope you find it useful.
000086CR : Clean Installation of Easy Media Creator
This solves many problems with Roxio/Sonic software...runtime error, xxx.dll, timed out...