Have you tried executing the proc from the isql command line tool that comes with ASE 15.7? [Objective is to rule out any issues with your C# program and/or Toad.]
The documentation on Msg 622 suggests contacting tech support. Have you opened a case with tech support?
A google search turns up this item on SAP note 1963568; while you're welcome to try the suggested resolution I'd also suggest a) taking a look at the details of the SAP note and/or b) opening a case with tech support. [Sorry, I don't have S-user access at the moment so I don't have the sap.com link to SAP note 1963568.]