Am I IM?
http://members.optusnet.com.au/~villaump/pevsoft.htm
I haven't had a chance to look over the latest PEV tools yet, but in the past I've fixed the first problem by opening the IM with PM2IM and "converting" it to IM even though it's already an IM. Main thing is have the "Strip Textures" checked on, then create IM, it will overwrite the original with a new IM that has faulty textures stripped out. Generally the cause of that is an error in the mesh, for example the original model creator assigned ash.texture to a.bucket1 on a conveyor belt then forgot to create the a.bucket1 attachment on the conveyor. Previous versions of Trainz merely ignored those errors.
Second item, "power of 2" means starting with the number 2, multiply by 2. So you have 2, 4, 8, 16, 32, 64, 128, 256, 512, and 1024, or even 2048 if you want to get nuts. A texture of 512x512 pixels is okay, or 512x128 or 128x32, it doesn't have to be square but the height and width have to be divisible by 2 all the way down to 2. That wasn't always the case, so some early models had textures that were (for example) 192x56 pixels, those numbers are not a power of 2. To fix those, find the closest power of 2 dimension and resize the texture in an image editor, for that example I would resize the 192x56 pixels to 256x64. It shouldn't distort anything, since the mapping will stretch or shrink the texture to fit the mesh.