Salesforce.com limits formula fields to 1300 characters. Once you hit the 1300 character limitation you have to split up your formulas into two to four separate fields.
You can do this by using the API Field Name of another formula field which contains Conga Parameters. Using the QueryStringField parameter, you will reference your QueryString formula field by its API field name in your Workflow formula.
Query String Field 1
Query String Field 2
The Query Strings connect the separate formula fields and pieces them together to work around the 1300 Salesforce character limit.