When I did my testing, I didn't have the technical specs custom field set up right. I'm now getting the same error you are on that film.
2 Days In The Valley
http://www.imdb.com/title/tt0115438/ has all the same tech spec fields, and it gets parsed correctly by the plug-in.
It's weird, and because the error is coming from a dll, there isn't anything to be done about it.
As to the original question...what is it and why does it happen...
"Probably" what is happening is that the plug-in in parsing the HTML code from IMDB using logic like:
- Find where the start of data is
- Find where the end of data is
- The data is everything between the start and the end
The problem occurs when the 'end' isn't found. The probable culprit is the POS function. If you're parsing a web page, and POS can't find the characters you define as an 'end' position, it returns "-1". If you have data like "this is data" and you get a start position of '0' ('t'...the first character), then you search for something like 'z' as an end position, you end up saying give me all the characters from the first position to the previous (-1)...obviously that can't work.