[V8i SS10] SID image file - "The file type is not supported"

I need imagery from Tennessee for a project that has come my way.

I was able to download SID files (sid/aux/sdw/sid.aux.xml) for the area of interest, but I can't attach them. I can select them for attachment, but then I get an error "The file type is not supported - [13]"

I thought we could use SID images? Are there versions that aren't compatible with V8i-SS10? Am I missing a step?
Other people are waiting on me for this imagery, and I have no idea how to get it.