[rivoli]

al my bumps are grayscale, saved in JPG RGB 8bits per channel, so it must be 24 bit colour.

maxwell doesn't like grayscale images, from your post i can't understand if you're using grayscale or rgb textures.
if they are greyscale just turn them into rgb, that'll solve the problem.
if they are rgb check that your map is actually turned on, maxwell tends to uncheck textures slots, it's a known bug:

http://www.maxwellrender.com/forum/viewtopic.php?t=4202

[sidenimjay]

there is a discernable difference between the texture uv being on the point or on the vertex of any given mesh. the difference is in the way the points and verticies are ordered, and they may not be in the same order on this particular mesh

since points can be consolidated, fused, smoothed or welded, depending on package in use, point counts and vertex counts can be different.

in houdini , i have the option of placing the uv on the point or on the vertex, but in the export to maxwell i only look for point uvs. this error looks similar to ones i have done where i promote a vertex uv to a point uv and my point counts are less than my vertex counts.

the transition from vertex uvs to point uvs can be tricky depending on how the geometry is being fed to maxwell.

i dont know which exporter you are using, but i expect the errors you are seeing are a result of the type of projection you are using.

perhaps you can dive into the ins and outs of the projection method you are using to find the answer you need

helpful?? i hope