>> So, either way, there is a bug here. The only practical solution at this
>> stage will be to alter the ReportBuilder.App so that it checks for
>> expressions that are >255 characters in length, and doesn't allow
>> them. I will put in an enhancement request for SP2 for this on your
>> behalf.
>
> Wouldn't it be an ever better solution to remove the 255 characters limit?

Possibly. I know which ER is more likely to be accepted though, as should everyone here who has been paying attention.