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Good Day Dam:
Got the following error when trying to save dates that I am not available.

Three dates worked and the 4th gave me the following error:Call Stack# Function Location 1()JROOT/libraries/src/Router/Router.php:1662Joomla\CMS\Router\Router->parse()JROOT/libraries/src/Application/SiteApplication.php:7613Joomla\CMS\Application\SiteApplication->route()JROOT/libraries/src/Application/SiteApplication.php:2434Joomla\CMS\Application\SiteApplication->doExecute()JROOT/libraries/src/Application/CMSApplication.php:3205Joomla\CMS\Application\CMSApplication->execute()JROOT/includes/app.php:586require_once()JROOT/index.php:51
Is this OSB Related. Used Firefox and could not log back in to the Administrator. Closed the browser and used Edge. Could log in and then the admin worked again.  

Is this a known J6 issue?

Hi Wynand,
I'm not sure about the issue you mentioned.
Please submit a ticket under the OS Services Booking category, describe the steps to reproduce the error in detail, and provide your site information along with an administrator account.
This will help me check and resolve the issue for you.
Best regards,
Dam