[asp.net] How to resolve Error : Showing a modal dialog box or form when the application is not running in UserInteractive mode is not a valid operation

You also encounter this if you run an Application on a Scheduled Task in Non-Interactive mode.

As soon as you show a Dialog it throws the error:

Showing a modal dialog box or form when the application is not running in UserInteractive mode is not a valid operation. Specify the ServiceNotification or DefaultDesktopOnly style to display a notification from a service application.

You can see its a MessageBox causing the problem in the stack trace:

at System.Windows.Forms.MessageBox.ShowCore(IWin32Window owner, String text, String caption, MessageBoxButtons buttons, MessageBoxIcon icon,  MessageBoxDefaultButton defaultButton, MessageBoxOptions options, Boolean showHelp)  

Solution

If you're running your app on a Scheduled Task send an email instead of showing a Dialog.