Well, I already got it fixed about an hour after it happened.
What I did, and oddly enough:
-Went to 'Grand Chase' folder
-Right clicked main.exe's properties
-Went to Compatability tab
-For some reason, 'Run in 640 X 480 screen resolution' was checked. I unchecked it.
-Checked 'run this program in compatability mode for' and chose 'Windows 2000'
Then it started to run just fine. o_o
Hope this works for someone.
Pinkie Pool's archnemesis: Oatmeal.