By default there are no error codes displayed when the installation of an application fails on Symbian. You only see numbers if you apply The ultimate* software installer debug guide but that trick doesn't work on E61i (and you would know in such case what 14 means).
So, when/where do you see this 14? And is it 14 or -14 (KErrInUse)? Is it really an install time error or a run time one?
And yes, you must install the Qt libraries, of the same version as those from which you took the demos from, before atempting to run applications/demos linked against those libraries.