Sharepoint - Activity 'DynamicActivity' has 51 arguments

So in SPD Workflow there is limit of using 50 variables. There are following options to solve the issue.

1. You can limit the number of variables to 50.

2. Increase this limit. So to increase this limit there is no other way then to update the database directly, that we strongly not recommend this to be done.

   Update WorkflowServiceMaxArgumentsPerActivity row in WorkflowServiceConfig table in WFResourceManagementDB by default value is 50 and restart server.

You can refer following links for further details:

http://social.technet.microsoft.com/Forums/exchange/en-US/56ee857d-e211-4570-8901-cd86a54ebdad/spd-2013-wf-error-maximum-number-of-arguments-per-activity-50?forum=sharepointcustomization

http://social.msdn.microsoft.com/Forums/sharepoint/en-US/3a08c175-1b3a-4a1c-beb0-b59c0a1b7a5d/2013-designer-workflow-with-lots-of-approval-processes-fails-to-publish?forum=sharepointcustomization#53454866-c87f-4704-ba08-964923012575

http://moresharepoints.blogspot.in/2014/01/sharepoint-designer-2013-workflow-error.html

Also you can increase the limit through powershell, run from an elevated prompt on the workflow manager server:

 Set-WFServiceConfiguration -ServiceUri https://wfserver.example.com:12290 -Name WorkflowServiceMaxArgumentsPerActivity -Value 75