Was support for Mr. Sid files dropped by MM. I haven't used it for quite some time, but now I no longer see that file type when I want to import a *.sid file.
I've not used mr sid files but when you goto add a layer you still get the option under file type (using the drop down box)to add a Mid sid (*.sid) file.
Ah Ha! I discovered that after replacing my computer a few months ago and downloading the latest Mr. Sid files, I never entered my registration code, and I didn't have the Pro features available. All's well.