This article was created in response to a support issue logged with K2. The content may include typographical errors and may be revised at any time without notice This article is not considered official documentation for K2 software and is provided “as is” with no warranties.


A Server Error appears on Runtime:

Argument 'userFqn' may not be null or empty
Parameter name: userFqn



The error only appears on Runtime and not on K2 Designer. Restarting the K2 Blackpearl service temporarily resolves the issue.

Troubleshooting Steps

To resolve this issue:
  1. Compare the K2 Designer and Runtime web.config files located in:
    ...\K2 blackpearl\K2 smartforms Designer\web.config
    ...\K2 blackpearl\K2 smartforms Runtime\web.config
  2. Ensure that lines below exist on both files:
       <deny users="?" />
  3. If it is not present on one, place it right below the </authentication> tag.
  4. Save and close the file changed.
  5. Perform an IISRESET.