Pier file upload problems: MessageNotUnderstood: PRViewCommand>>fields

I have tried Pier2 and the new PierAdmin but I keep getting an error when I try to upload an image file (I have also had the error when I try to edit the footer layout). I am running on MAC OSX snow Leapard, But have also happens on an Ubuntu installation in VirtualBox on my Mac, and on a separate PC with Ubuntu installed. has anybody seen this error before? (please see debug print below)  - I hope somebody can help?

Many thanks.


Seaside Walkback

MessageNotUnderstood: PRViewCommand>>fields
Debug Proceed Full Stack

Possible Causes
you sent a message this type of object doesn't understand
Stack Trace
thisContext
PRViewCommand(Object)>>doesNotUnderstand: #fields
self
a PRViewCommand[270270464]
thisContext
PRDocumentWidget>>text:
self
a PRDocumentWidget
thisContext
[:value | self text: value] in PRDocumentWidget>>renderEditOn:
self
a PRDocumentWidget
thisContext
BlockClosure>>valueWithPossibleArguments:
self
[:value | self text: value]
thisContext
WAValueCallback>>evaluateWithArgument:
self
a WAValueCallback
New Session Configure Halos Profile Memory XHTML 4/10 ms

* I tried the stack VM with the pier image, it seems to have solved the problem (but I only gave it a quick test.)

I tried standard Pier2 oneclick on the Chrome browser and the problem went away, tried again on Firfox and the problem came back - it might be Firefox or my particular settings in Firefox...

SOLUTION (?):
If I disable cookies in the browser prefs it solves the problem, at least when I tested it for about 20mins,  cookies on: the fault came back, cookies off: the problem went away. (repeated the setting several times)

Has anybody else seen this problem? I have not had any comments re this post at all.