It seams that CX is reserved word in Cognos Express and you can't name host CX...
I installed CX and standalone server and named it "cx". When I was trying to connect to Report Studio or Xelerator, using address http://cx:19300 I was getting error DPR-ERR-2079, Through address http://localhost:19300 everything was working fine.
When I renamed host to cxtest (CX of course stopped to work and I reinstalled it) address http://cxtest:19300 also started to work.
P.S. CX configuration could be more flexible... :(