Google calendar has always been slightly more particular about ics feeds and frustrating in the lack of information it gives if it rejects a ics url. Thanks to Toby Hage, a couple of oddities to do with blank lines in descriptions and in repeating dates (RDATES) in the ics feed were been identified. These are now resolved in version 3.11. This version is up at http://test.icalevents.com/ and all appears to be stable so far. It is available for download at http://icalevents.com/downloads/amr-events/
If any of you have any feature requests, please contact me at firstname.lastname@example.org.