Well, that's getting a bit closer! Thanks for the info. I'm now getting the following error:
XQE-PLN-0286
The second argument to the 'cast' function is a character data type with a size that exceeds 65535.
The expression is: cast(substring([BLOB Data Item],1,93000) as varchar(93000))
I also tried: cast(substring([BLOB Data Item],1,65000) as varchar(65000))
The BLOB text field is approx. 93K characters.

Its huge, I know.