Hi all,
I found this problem also, and, well, I wrote a nice little post on how sometimes textures just don't work etc. etc but then I thought of an issue from back a bit and tried the solution...and it worked. So I deleted that unhelpful post and am posting a solution instead.
For some unknown reason, a few textures will not apply correctly (on some systems) even though all is installed correctly. The solution for some of these obstinate textures is to copy them to the main FSX\Texutre folder. In this case, the textures for the airmail_depot, fbo_1, fbo_2 and fb0_3 object are:
airmail depot.bmp, airmail depot_LM.bmp, FBO 1.bmp, FBO1_LM.bmp, FBO 2.bmp, FBO 2_LM.bmp, FBO 3.bmp and FBO 3_LM.bmp
Go into the EZ Scenery Libary Texture folder and copy the above .bmp files into your FSX\Texture folder and you should be set to go.
Worked for me!
Rod