I couldn't find any explanation about these tags in the xml reference...

<MTSTimeElem Type="ResetVerts"
<MTSTimeElem Type="MTSBoner"

this might be construed as an hilarious question...but let's not go there.

These elements are part of the morphing code which Poser ProPack creates/outputs when publishing a Viewpoint scene.

"ResetVerts" refers to resetting the vertices of an object to its original state. The MTSBoner refers to the bone structure of an object...which VET doesn't support (no internal bones).

Much of the code which Poser creates is outdated and improper vs. today's methods of delivering a Viewpoint scene.

My recommendation would be to carefully extract declarations, animations, and etc. from the Poser delivered scene...placing them into a clean new VMP scene which is tried and true, or just plain new and properly established.
hth
DavidR