RoboHelp HTML -- cannot check out image

Hello,

(First of all, we use version control.)

The problem: one .gif image cannot be checked out. The help system has several .gif images, and all the others can be checked out.

When I access my images through the "images" directory (in the left-hand pane), usually I can right-click an image and see the option "check out [file name]" (or "check in"); but for this particular image, that option does not appear.

Nor does the image check out when I open the topic containing the image.

I checked the RoboHelp help system, but to no avail.

It's probable that deleting the problem image file and re-inserting it would work; but that is a only work-around and doesn't help if it happens again.

What can you tell me about this problem?

Thanks,

Chris