Anvil embeds reference to a script in your 3ds Max scripts folder. If that file is missing, there can be an error.
Anvil embeds some scripts for scene startup to protect displacements from being invalidated via improper manipulation. Older versions of Anvil referenced a file that could cause an error if missing.
$jigglebones are bones that can automatically generate secondary motion without being animated. Making a $jigglebone in WWMT requires you to use the hierarchy tab in the command panel, which may be a new area for less experienced modelers.
This error occurs when the path for the output model does not exist. This is an error that happens at the compile stage and will happen if you are compiling straight from WWMT or by compiling manually from the batch file.