Do you have the latest imagemod componentpack installed?
Not having all the images would be a good reason for the error message. Something like "Can't open comp887.bmp", I presume?
The marker components are almost certainly there so that when you are on the research screen and right-clicking tech areas to see what they give, you will see an entry for the mount.
EG: "Expected results: EB mount"
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What to do:
1) Download the latest componentpack from one of the imagemod mirrors:
http://imagemodserver.mine.nu/other/MM/SE4/imagemod/
2) Extract the extended picture set to your SE4/Pictures/Components folder.
Note: There will be one file it asks to overwrite: components.bmp.
This is OK. The components.bmp included in the zip is completely backwards-compatible.
Note2: Installing to the SE4/pictures/components folder is what the imagemod is designed for. It will not affect your unmodded game, and ALL mods will be able to use the extra pictures provided.
Don't bother putting it into SE4/STM/pictures/components, as that will just waste your disk space.