I've had problems whenever any of my libraries exceeds 250 folders by much. I go thru & consolidate contents to reduce the # of folders regularly - usually using Yarp's P3d0 program. I've also "moved" a lot of MAT & MOR folders over to the Camera & Lights libraries - they'll work just fine from there, but the File Extensions have to be changed from PZ2 to LT2 or CM2 so Poser will "see" them there. There's a fine Commercial Product called PBoost that "swaps" groups of folders into & out of the libraries when needed. - works differently for some folks depending on their computer & OS, but there's a free Compatibility tester in freestuff, last time I looked.