The file opened by WED contains no valid WMP content. There can be a couple of reasons, like a PC crash during saving, a harddisk fault, or manual editing / overwriting of the WMP file. If the WMP file is destroyed, it can be recovered: WED automatically produces two backup files, a .BAK file at each save operation, and a .$$M file at each BUILD operation. The latter is only for emergency cases, as the group information is lost.
The map is way too big or contains too much or too complicated polygons to be compiled. Erase a lot of blocks. Replace block objects or prefabs by map entities.
The map contains bad blocks or other problems. If block errors were indicated before, erase those blocks. Other problems might be too elongated or acute blocks.
The compiler does not like the shape of a particular block. Mostly harmless.
A block has an edge that is too short - two vertices are too close to each other. If the block number is given, find that block (Edit -> Find Block) and erase it.
The block is ill-shaped, or has duplicate planes or some other problems. It won't be visible in the level, and can produce portal errors. Find that block and erase it.
You have tried to update the textures of a map, but the level itself or a texture size has been changed. The map must be rebuilt.
You have tried to apply passable (liquid) and solid textures to the same block. You have to decide whether the whole block should be liquid or not.
You have surfaces in your level which are too big for the rendering mode selected. Extremely large surfaces should be rendered in flat mode, otherwise they will consume too much memory and reduce the frame rate. You can ignore the warning, but then the level will be very slow in compiling and rendering.
The given block has two identical, or very similar sides. Find and erase it.
Block x is too narrow. Use Object>Find Block and make it bigger. Often followed by Warning W075.
Two identical blocks at the same position, probably due to a failed copy operation. Another possibility for creating duplicate blocks is moving one block inside another and then performing a Subtract operation. Erase one of the blocks.
The block x is not big enough to be a convex block. See also Warning W072.
The sky box is not completely closed, or an object is outside, or a large object - like a terrain - is penetrating the sky box, or there is no sky box at all. This is normally not a problem, but can increase the compiling time. However the outer surfaces of the sky box should have the NONE rendering mode set in such a case to prevent a frame rate decrease due to scanning invisible surfaces.
An internal error occured that could lead to a clipping problem in the level at a certain place. Mostly due to block errors that were indicated in previous warning messages. Mostly harmless.
The texture is applied to a surface that is too large or too small, or belongs to an ill-shaped block. The surface will be displayed with a default texture.
An internal error occured that could lead to a clipping problem in the level at a certain place. Mostly due to block errors that were indicated in previous warning messages. Mostly harmless.
A block has an edge that is too short - two vertices are too close to each other. If the block number is given, find that block (Edit -> Find Block) and erase it.