Actually, I think Poser just continues searching for the other files down the list , especially if the external runtime is not added to Poser's runtime libraries.

It will appear to hang for a very long time, by which time Pluto has orbited the Sun several times. After which, it will show you the usual working window and User Interface.

You could edit out the culprit reference to a non-existent file, by opening the uncompressed content file and removing the filename in a text editor.  For example, you have a prop which keeps telling Poser to look for XYZ,jpg. and you have confirmed that there is no XYZ.jpg anywhere in your hard disk.  OK.

If this example is a compressed prop file, ask poser to uncompress it ( from the drop down menu ).  If it isn't then just flip it open using a text editor - I use MetaPad.

Do a search for that XYZ.jpg string, and delete every reference to it.  re-save.

Eternal Hobbyist