To import them I do what I have stated above either opening an existing project or starting with a new empty project; File<Import<browse to and select files (either all of the files or by choosing JP2 from the drop down then selecting all of the JP2 present<import< nothing happens.
OK. Do you press the "import" button after highlighting them? This may sound absurd to ask, but when tracking down which detail is the issue, literally every detail has to be mentioned.
Also, where is the focus in the project when you do this? Is the focus on a read/write portion of the project, or are you within a read-only data source (which will not allow any imports)?
Here's what I do, the absolute most simple procedure (add variations when you have the procedure below working):
1. Launch Manifold. It opens with a new, blank project.
2. Choose File - Import.
3. In the Import dialog, navigate to where I have my .jp2 file.
4. I double-click the .jp2 file I want to import. I don't double-click anything else, just that one file that ends in a .jp2 three letter extension.
It imports fine.
Note that some older .jp2 files have the wrong channels assigned (that's an error in the file, not in Manifold), so sometimes you have to use the Style dialog to switch channel ordering from BGR to RGB.
Ah... one last thing:
If you get but when I double click on them to open them i get - Unspecified MrSid error:1 when linking a file, that same file won't import at all since the MrSID code cannot read it. That usually indicates:
a. The file is not a .jp2, despite having that extension.
b. The file is a .jp2 variation the JPEG2000 driver (which is third party) doesn't understand. Can happen when people modify a .jp2 with third party software that writes the modified version in some weird variation.
c. There is an installation on your computer of some other software that uses a different JPEG2000 driver which is ahead in the PATH and thus is conflicting with what Manifold is trying to use. (I don't think this is it, just guessing out loud).
See notes in theJPEG2000 topic on the SDK used, as well as the link to ECW in that topic.
Whoops! I see adamw has likely identified the issue.