Try two things
1) Restart the game and try again
2) If you get same error - find the location where you have installer the game, for example:
C:\Program Files (x86)\Reverie World Studios\Dawn Of Fantasy\
Inside locate a file DoFUpdater.exe
3) Right click on the file and choose "Run as Administrator"
this might fix. Let us know if this doesn`t work and I`ll get one of the programmers to help you.