Unintentional Auto-update to 2.0.26d - PROBLEMS

[Sadruddin]

I seem to have done an auto-update to 2.0.26d from 2.0.20a

I now have a SERIOUS couple of problems.
Front end seems to work fine, but the cart - intending to pay - is blank, with just a url bar http://www.interfacepublications.com/site/index.php/component/virtuemart/cart?Itemid=0

Erm.  Help?

Also, what I was TRYING to fix was a problem with PayPal Standard options returning

"Please check your server that handles PayPal Instant Payment Notifications (IPN). Instant Payment Notifications sent to the following URL(s) are failing:

http://www.interfacepublications.com/ipn_main_handler.php

If you do not recognize this URL, you may be using a service provider that is using IPN on your behalf. Please contact your service provider with the above information. If this problem continues, IPNs may be disabled for your account."

Looking at a post on this site, it looks like PayPal was re-written for this version.
Is that right?  And if so, what do I do next?

[John2400]

Hi back up and back up again.

now download your old version- and reinstall it over the top.

http://dev.virtuemart.net/projects/virtuemart/files

also the paypal issue is spoken about throughout the forum. My understanding is that it will be fixed in an update.

or there is a path I see in a forum post here to maybe fix your issue - read the post well and then proceed here:

http://forum.virtuemart.net/index.php?topic=121585.msg414953#msg414953

now back up your new version of you site.

[Sadruddin]

Whew.

Well, that's fixed the cart page.
I'll have to do a careful gradual upgrade through the various versions, I suspect.

I'm not sure that that link is about my problem.
That thread seems to relate to an error in 2.0.26d, while mine seemed to have spontaneously appeared still in 2.0.20b.

There do seem to be a few references to this when googled, but not so much on VM.
And at present it's making my site unusable.

[Sadruddin]

PS.  THIS fixed it

http://forum.virtuemart.net/index.php?topic=92546.msg387426;topicseen#msg387426

Thanks.

However, I now have to negotiate a number of upgrades.
From 2.0.20b to 2.0.26d, to be precise.

Is there a thread which will hand-hold me through the process (including pitfalls), please?

[jenkinhill]

Check the live update info:  http://virtuemart.net/index.php?option=com_content&id=416

Main issue can be with commercial templates and one page checkout changes:  http://forum.virtuemart.net/index.php?topic=120943.0