Unable to fetch connection string to retrieve data

Hi Folks,

I am using connection string to fetch document details which i have uploaded in folder. When i execute/Test connection string to retrieve data its working. But if i call the same to fetch details dynamically from process model its not fetching. i am getting the error as "[workflowVariables:[FileName:[Document:]],status:ENQUEUED]"

When i execute individually with hard coded value getting correct result as " [workflowVariables:[FileName:[Document:36161]],status:SUCCESS]"