Insert > Picture > From FIle gif sometimes works, sometimes doesn't

[SteveK]

I am making little gif images of icons (screenshots from other applications)
that I insert into Word. I am using Insert > Picture > From File to insert
them inline between text. Sometimes it works, and other times I only get
the broken image icon.

I create the gif by taking a screen shot, then bringing it in to Corel
Photopaint, then crop and export to gif. I always use the same settings for
the gif but some images work and some don't. I don't know why this would
be.

SteveK