Bizarre error with cmd.CreateParameter

[audleman]

I am trying to pass a text string into a stored procedure via a
parameter, and am getting the baffling error:
adErrDataConversion 3421 You are using a value of the wrong type for
the current operation.

I know for sure that the data type I've selected is correct. The code
looks like this:

Set plsShare = cmd.CreateParameter("@shareIdeas", adVarChar,
adParamInput, 500, trim(Request("Please share your ideas")))

The crazy thing is that it only throws this error 1/20 times the
procedure is submitted. The last time it failed, the text string passed
in was:

always share a brief inspirational reading/statistic at beginning or
end of the class and establish a theme around which you teach your
material. Everything has a story.

Can anybody explain this error?

Thank you,
Kevin