If the reload of a qlikview document fails then the first place to look is the log file of that document. That log file can be found in the same place as the .qvw document. It will have the same name with .log appended. If that file does not exist you need to enable the option Generate Logfile on the General tab of the Documents Properties window.
What can I add when the two community maestro's have already provided their invaluable wisdom
Could you provde us with some server details? What version of QVS? Are both QVS and QDS running on the same machine? How much RAM is configured in the machine(s) running QVS & QDS? How big is your document?
You seem to reload your document while users are visiting the access point, which could pose a conflict of (RAM) interests if both QVS and QDS run on the same machine...