This happens because the user who uploaded the MXM to the material gallery placed the textures in a folder relevant only to their machine, so on your machine MXED won't be able to find the textures. To fix this:
- Go to the folder where you downloaded the MXM and double-click it to open it in MXED.
- MXED pops up a dialog asking you to locate the textures used in the material
- Navigate to the folder where the textures are located and choose the missing texture. If other textures used in a material are located in the same folder, MXED will continue searching in that folder for the other missing textures.
- After you have made sure all the textures are found (go through each BSDF in each Layer of the material to make sure), click the Save & Close button (the little CD icon) in MXED to save the MXM with the new texture paths.
- Verify that all the textures are found for the MXM by double-clicking the MXM to open it in MXED again. No missing textures dialog should appear.
MXED/Maxwell Render/Maxwell Studio will look in the following paths to find the textures of a material:
- in the same folder where the MXM is located
- in a 'textures' subfolder where the MXM is located
- in the project folder (ie where the MXS file is located)
- in the texture paths specified in Maxwell Render/ Maxwell Studio preferences. To set these paths, go to:
- File>Preferences>Paths (Maxwell Render)
- File>Preferences>Materials>Textures (Maxwell Studio)