Issue
When trying to create a workflow in any 2010 mode site on a 2013 Farm, the following error might occur:
at System.Web.UI.MasterPage.CreateMaster(TemplateControl owner, HttpContext context, VirtualPath masterPageFile, Dictionary contentTemplateCollection)
Error Code
Additional Information
This error indicates that the copy of the Nintex WorkflowDesigner.aspx pages in the 14 hive are incorrect.
Resolution
Redeploy the solution named NintexWorkflow2013BackwardsCompatabilityUI.wsp. To do so, navigate to Central Administration > System Settings > Manage Farm Solutions.
Additional Information
Redeploying the NintexWorkflow2013BackwardsCompatabilityUI.wsp solution with correct the NintexWorkflow files in the 14 hive.
If the error persist, retract the NintexWorkflow2013BackwardsCompatabilityUI.wsp solution and attempt to deploy again using the following PowerShell command:
Install-SPSolution -Identity nintexworkflow2013backwardscompatibilityui.wsp -GACDeployment -CompatibilityLevel 14 -Force
Note: the "-Force" operator should only be used as a last resort.