As hinted earlier, the problem is because WC3 has a file path limit for custom game list search. What is even worse is that this limit is the entire file path so that your system locale and build type affects the maximum map name length.
I have seen maps online that I could not play because the file path was a few characters too long due to someone playing on a x86 system while I was playing on a x64 system (where there is an extra " (x86)" in one of my folder names).
For this reason you should try to abbreviate your map name and only append a version number.
Instead of...
"World of Epilore - Mage Campaign.w3x"
Call it...
"WoE - MC.w3x"