The setup is something like this:

6 Citrix servers, to which users are randomly assigned at logon.
I assume this has something to do with automatic load balancing.

The app itself resides on an application server.

The error occurs randomly, sometimes on one, sometimes on several Citrix servers at the time, but can, once it occurs, be consistently reproduced on said server(s) until they are rebooted.

There is nothing obvious in the code, that (at least to me) would explain why.

For instance READ EVENTS or

IF CURSORGETPROP("SOURCETYPE") = 1 OR CURSORGETPROP("SOURCETYPE") = 2

can fire the error, which in general seems to wander all over the application.

Hopefully none of the above can be considered to be spectacular transgressions of any kind?

Anyway, this is what happens.
All help appreciated!

Peter