Ok, just in case anybody is interested I figured this out as being a case of songs which for whatever reason didn't download/synchronise correctly over the air via wifi/3g to my iPad.
I basically found this out by accident, after erasing all content on my iPad I checked it's status in iTunes and was pleased to see everything had now gone, so I started adding songs and while doing this the cable came out from the iPad and I was left with greyed out songs with the circle on the left, however this time I was able to delete them and then add them to my iPad correctly.
So to recap then the only way to be able to resolve this if you have this issue is to do a factory reset of your iPad, unfortunately even restoring my iPad from an iCloud backup resulted in this issue still occuring so I backed up Apps that I could and dowloaded the rest.
Hope this helps someone in the future.
Steve, I was having a similar problem with a video file and found your thread.
Then I realized that duh, I already had a solve for this!!! Must be getting senile.
It's from 2012, but I just tried it again and it resolved my latest issue: https://discussions.apple.com/message/17335749#17335749