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You're using XOOPS 2.0 RC3??? That's a year old! I strongly recommend you start using XOOPS 2.0.6, the latest release. XOOPS2 RC3 is a Release Candidate, meant for debugging and testing, not to be used on live sites and in production environments.
The general rule for reporting blank pages is to turn php-debug on on the system admin -> preferences -> general settings page, and report the errors displayed on the blank page. That way we can see what is causing the rendering to break and determine a solution.
Herko