Hi Jimmy
Thanks for your response, I have read that the error means that a rule is being fired repeatedly and I can see it is but I don't understand why or how I can avoid it. This only ever occurs when there's a carriage return / line feed in the text box. It's also very easy to replicate.
Add a text box to a new InfoPath form, enabling the Multi line property.
Add translate(., "abcdefghijklmnopqrstuvwxyz", "ABCDEFGHIJKLMNOPQRSTUVWXYZ") to the formula property.
Preview and enter text with a Carriage return/ line feed and some more text, you should get the error when the field losses focus.
This error will also occur if you remove the formula and insert the following JScript code in the text box's after_change event.
var value = XDocument.DOM.selectSingleNode("/my:myFields/my:field1").text;
value.toUpperCase();
XDocument.DOM.selectSingleNode("/my:myFields/my:field1").text = value;
Seems very weird to me :)
I guess I may have to split the text box into separate fields which is a bit annoying!