I had the same issue too, but found a solution. Go to your zm_mapname in Radiant. As you enter, look for a white textured character model around your map. If you have player spawn boxes in your map, click on it and it will coordinate you to where the model is. Click on it and delete that. Save, compile and it will work.

I had the error as well, and yet this solution didn't work for me. I found an all-white model of a human looking character standing somewhere in my map just like you said, but the strange thing is that I can't select it by shift-clicking or any other method I know of. The model appears in the "All in Use" tab under models, but the one I can't select is the only one I can find (Whenever I drag in another version of that model from the "All in Use" tab it works fine and I can select it so the problem isn't with the model itself). An even weirder thing is that I couldn't even see it initially except for its shadow. The shadow is the only way I could have found it actually because you can't see the model (except for the shadow of it) unless you hit F9 and go into Game View. Also, I tried selecting the spawn boxes like you said to see if they would lead me to the model, but in fact nothing in my map leads to the model. It's almost like its a ghost model. Like I can see it there even without it being present in my map. This is really frustrating and I'm not even sure this is the real problem.
Please help! Thanks.

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Double Post Merge: November 04, 2016, 11:26:41 pm

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UPDATE: I figured it out, but there's another problem. I solved the first problem by doing the following: If you open the "entity list" window (by right-clicking on the toolbar and clicking "entity list"), you can select entities from inside that window. I was able to select the white textured actor from in there and delete it successfully. I don't know why radiant wouldn't let me select the model in the camera view but oh well.
However, this seemed to cause another problem. Even though my map was able to render successfully without errors, and I was able to load into the game without it crashing, There was no music as the map starts like it normally plays. Also, no zombies spawned even though i was in the game messing around for about 5 minutes. I'm guessing that deleting the white-textured model caused the problem because the spawners didn't know what model to spawn or something. I'm not an expert on this so that may not be the case, but my intuition says I'm correct. Any help on this would be appreciated. Thanks.