Ok come to think of it periods aren't really important, as long as I can tell between session marks and lesson marks, this report doesn't seem to include session marks anyway.
When specifying the .xml in the output arg in CLR it appears to only produce the schema version of the xml report.
It looks like I am actually getting somewhere now, thank you so much you are a life saver! I'd come to far to give up, I'd written my own XML parser in php; capable of parsing huge files (we're talking gigabytes) in order import data from these reports into a mysql database.
My next step is to be able to produce a fresh paramdef.xml file using php to define the between dates. How did you produce this paramdel.xml file?
James