Products: Nintex Forms 2013, Nintex Forms 2010
The following error appears when loading up Nintex Forms Designer and is logged in ULS logs:
The Expression prefix 'NFResources' was not recognized. Please correct the prefix or register the prefix in the <expressionBuilders> section of configuration.
The following errors appear in the logs:
The issue occurs when the Web Application Feature for Nintex Forms needs to be activated.
Use the following procedure to resolve this issue.
1. On the Central Administration Home page, click Application Management.
2. In the Web Applications section, click Manage web applications.
3. In the Name column, select the web application on which you want to activate Nintex Forms. For example, select SharePoint -80.
4. In the Web Applications ribbon, click Manage Features. The Manage Web Application Features dialog box appears.
5. In the Nintex Forms section, click Activate. After a short delay, the dialog box refreshes and the status is "Active."
6. Click OK
Note: For more information please review page 22 of the Nintex Workflow & Nintex Forms installation guide: Installing Nintex Workflow 2010 and Nintex Forms 2010 Installing Nintex Workflow 2013 and Nintex Forms 2013