It is most likely a problem with the MAX2GS exporter. This has happened to me in the past and may have to do with the way the texture is applied to the block. Sometimes the MAX2GS exporter will create invalid size or positions for textures and this results in a non-textured (and thus, invisible) block. There are a few ways to test this:

1 - Select the block in WED, scope down to a face and then look at the texture properties.

If a texture is 128 x 128 then it cannot be moved along the X or Y axis more than 128 or less than -128. I have had, in the past, MAX2GS produce a strange offset number like -345 on a 128 pixel texture. The engine will not understand this as it does not see the sense in moving a tiling texture more than its pixel size (which only makes sense).

2 - Make sure that QUIET mode is not checked when you build.

You will want to look at all the errors produced. They will give you a hint as to what is going on.

3 - Open the level in MAX and apply a different texture and do not do anything special to it.

Then export the level again using MAX2GS and see if the problem is solved.

Let me know if any of this helped. If not, we will explore a few more possabilities. Oh, if you find out that MAX2GS is the problem, report the bug to Martin (the creator of MAX2GS). He is good about fixing bugs when they are faithfully reported.