I'm the most novice of novices when it comes to this software...so please be gentle. Pretend like you're explaining this to a fourth grader. I'm serious.
I am trying to reopen a file I saved as .idml with CC. It was originally created in CS6, but the .idml file cannot be opened in that version either. It tells me I need a plug-in in the error message when I try to open it in CC, but I just don't know what that is.
Send help. On a deadline. Thanks in advance!
Unfortunately, you probably made a rookie mistake. Instead of *exporting* your document to another format (in casu, the IDML format), you *saved* it 'as usual', only changing the extension to ".idml". That, in itself, does not make it an IDML file (much like 'saving' it as ".JPG" would not make it a valid JPEG image).
If you are now working on CC, renaming the file back to .indd ought to solve it. Poor InDesign gets confused because it thinks the file you feed it "is" an IDML file ... and my bet is, it is not.
Footnote: It was not necessary to (attempt to) save an CS6 file as IDML in the first place ... Newer versions of ID can open older files immediately. Only when the jump 'from' a very old version is larger than 2 or 3 versions, it is generally recommended to use an intermediate IDML.
Yes, thank you Jongware, this is exactly what I did - the "save as" option. I was unaware until browsing desperately in the help articles that 'exporting' was an option. Thank you for the peace of mind.