You might need to take it in smaller batches. I'm assuming you're using XML Checkpoints for your validation? If so, that means there's 150 XML check point log items in your test log, each one documenting a validation result for each tag within each XML file. If each XML file has a minimum of 40 tags, that means you're looking at a LOT of data to be parsed and displayed.
Something that might help is for you to use the Compare method with "ReportDifferences" set to false. This will record that there WAS a difference but won't report the details of the difference, thus reducing the size of your log file.