It's believed this is caused by Windows "Background Activity Monitor" It's supposed to prioritize network traffic on the computer. Library loads work through the network even if the library is local. (The library window is really just a stripped down Chrome web browser.)

The "BAM" seems to incorrectly force all the library processes into a background thread. If you're brave (or crazy) the relevant registry key is here:

Computer\HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\bam\State\UserSettings\

Cleaning out all references for Poser in that key seems to rectify this condition. And, don't even try it unless you know what a registry key is and why messing with the wrong one will crash your computer.