qer_editorimage textures/emerald/emerald_view.tga is for radiant only. The actual textures are indicated by skyparms env/emerald/emerald - -. You should have an env/emerald directory that contains the 6 environment map textures: emerald_bk emerald_dn etc..
It is possible that Radiant can't load the qer_editorimage and/or that Tremulous can't load the environment map but these are two different issues.
You can point the qer_editorimage to one of the textures, or use a different image, like a thumbnail of the skybox. In any case, it won't be used ingame.