Sys.FormatException
Raised by the Microsoft Ajax Library framework when the format of an argument does not meet the parameter specifications of the invoked method.
Remarks
When a client function or method is invoked and the format of an argument does not match the format of the corresponding formal parameter type, a Sys.FormatException object is created by using the Error.format function.
For more information about how to handle error conditions, see Debugging and Tracing Ajax Applications Overview.