Just a FYI for those who have xml errors. I must say I gave up with the free addons for Google Base, including the OC included extension, and purchased the one from UKSB which is excellent, as is Simon's support.
However, I still saw failure with XML errors. BUT using UKSBs extension I was able to select the options to 'Remove Non-English Characters' which fixed the xml errors and into Google went the products. However, only 85% of the products went.
After a lot of time studying the problem (coz I'm a bit slow) I discovered the reason for the xml errors, for me at least.
Some products do not have a description! Why you may ask. Many products we sell are self explanatory by the 'name' so no extra information is needed. However, to cure the Google issue we will simply replicate the data in 'name' into 'description'.
I hope this helps someone one day who is at their wits end with xml errors. In short Google hates white space in any fields it is reading in your product feed.