[Seaside] What does this error mean?

[David Pennington]

I am running Instantiations VAST 8.6.3 with Seaside. I am currently the only known user of the web site as I am developing a back end to an Android app and haven't got any other users. 
This is what is coming up in the debugger at random times.
On most occasions this seems to stop Seaside working so I have to close down the smalltalk and rester the image again.
Can anyone give me a handle of what is causing this error, please?

David

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