Error "The control type 'Nintex.Workflow.ServerControls.ApproverSecurityCheck' is not allowed on this page"

ISSUE

When editing a Request Data task, the following error might occur:
Additionally, the following error appears in the ULS logs:

RESOLUTION

Web.config entries need to be re-added, either through re-activation of the Nintex features or manually. Navigate to Central Administration > Nintex workflow management > Web application activation.

 

Note: Make sure to tick "All Content Web Applications".

 

If this doesn't work, add the following entries to the web.config file of each Web Front End server:

 

<SafeControl Assembly="Nintex.Workflow.ServerControls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=913f6bae0ca5ae12" Namespace="Nintex.Workflow.ServerControls" TypeName="*" Safe="True" />
<SafeControl Assembly="Nintex.Workflow.ServerControls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=913f6bae0ca5ae12" Namespace="Nintex.Workflow.ServerControls.WebParts" TypeName="*" Safe="True" /

ADDITIONAL INFORMATION

This is caused by missing entries in the web.config file of one or more Web Front End servers in the Farm.