I'm getting the following error when trying to active survey in closed access mode:
 
500: Internal Server Error - Database error!
An internal error occurred while the Web server was processing your request.
Please contact Administrator to report this problem. 

The survey automatically goes on to activate in open mode.

Using Version 6.16.9+260217 

Please help us help you and fill where relevant:
LimeSurvey version: [see right hand bottom of your LimeSurvey admin screen]
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Survey theme/template:
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