BizTalk Table Looping / Table Extractor error

I have been stumped by an odd error when using the Table Extractor combined with a functoid in BizTalk 2006 R2.

When connected to the destination schema I do not get any errors when testing; but when I attempt to connect the output to a functoid for further work I received this error:

Perplexed I've fiddled around for a couple of hours trying to figure out what exactly is going on. The XSLT generated behind the scenes essentially makes a variable for each of the outputs from the Table Looping Functoid, and tags an incremental number on the end of the variable name. e.g. $var1

In this instance the variable name didn't appear.

It then slowly dawned on me that when connected to the destination schema I wasn't actually seeing anything coming out - this pointed me towards the school boy error that I was attempting to address column 9 of the Looping Grid, when I had only defined 8 columns.

As strange errors send me running to Google, I hope this helps somebody else if they experience the issue.