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If you are in a page (not a block) of a module, the XOOPS core retrieves module configuration variables and places them in the global variable $xoopsModuleConfig in /include/common.php
The configuration variables defined in xoops_version.php are stored in the XOOPS DB when a module is installed. Also, XOOPS creates a link in the administration menu for the module labeled "Preferences" where an admin can manipulate those values.
For your problem, if you turn on PHP debugging in System -> Preferences do any error messages appear on the page using your $xoopsModuleConfig variable?