This could either happen, whenever the scaling of the textures is wrong, (check how the texture is scaled on the block) or you should try to recompile the level (do not use update textures, this option does not really work)
So this tells you, that it is a problem with the specific level, not the textures.
How big is the wall and ground blocks? Too big blocks will cause troubles, also check how the block is "seperaded" by the BSP (use f11 until you can see the red-lines when running you level)
if i does not work, put you level online for others to check.