Issue

Users accessing Internet via Draytek Vigor 2820 router occasionally get following message in their browsers and can not longer access Internet:

You have reached the maximum number of permitted Internet session.
Please close one or more application to allow further Internet access.
Contact your system administrator for further information.
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Closing applications or restarting a device, doesn’t resolve the issue.

Resolution

Few days before users started complaining about this issue, I updated router’s firmware 3.3.7.7. It seems that the issue is a bug in Draytek Vigor firmware. The error went away after downgrading firmware to 3.3.7.6.

Draytek Vigor 2820Vn