Well said indeed, Don. One does have to ask whether a dishonestly-conceived thread can really be a good thread. There are two threads currently active on TheSession to do with learning by ear which were honestly conceived and which are brilliantly productive.

Anyhoo:

Keith wrote I believe I can play reasonably well from the dots and remember/learn tunes by rote, but can no matter how hard I try, I cannot play in a session well.
I loose the tune if someone is not playing the same as me and once lost, although I may know the tune well, I can not find it again, anyone else have this problem

You hit the nail on the head. Learn a tune from notation, or even from just one particular recording, so that you can play it at home confidently, then take it into a session. You're toast! That is perfectly normal and is what is to be expected. It happens to me whenever I pick up a tune from a CD. The best way to learn a tune is to learn it from people playing it in your actively-listening/interacting presence. You can't always wait for that (I know - I live in the middle of nowhere in an area in which people who play Irish tunes are like rocking-horse shit). Stick with it, though, and dismiss any notion that might be lurking that you're right and they're wrong! Eventually you'll still be screwing up, but you'll be screwing up with insouciance!