Question: I am writing a parsing method for a csv record and want to throw an exception if the number of fields in the record do not match the expected length. 

What exception should I throw?

Answer: 
You could create your own exception class with expected/actual fields
If you want a built in one [InvalidDataException](http://msdn.microsoft.com/en-us/library/system.io.invaliddataexception.aspx)  is a good choice. Description:

`The exception that is thrown when a data stream is in an invalid format.`