QeRadiant, the editor for Quake 4 doesn't like Anti Aliasing being turned on so it'll often report various types of 'failed wgl' errors (ERROR: wglMakeCurrent failed). Make sure you turn AA off - either in your graphics card control panel or in Radiants preferences - where applicable.
[update thx AEon]
You should also consider turning off Anti Aliasing as a first port of call if the editor grid goes "strangely mushy" - the lines basically don't appear as clear and well defined as they should be or you expected.
Anti Aliasing basically 'blurs' on screen pixels to smooth out edges (which is how it deals with 'jaggies' or 'saw edge') of objects onscreen, this causes the lines to 'bleed' or otherwise loose their definition. Turning off AA should fix this.
Additional causes for the wglMakeCurrent error
There are a number of potential 'false positive' causes for the "wglMakeCurrent" error message, including, but not limited to, running the editor on Windows Vista (usually Direct X related driver issues) and/or using a Multicore CPU.
