Error handling can be controlled in SeoTools.config.xml where you can specify how errors (called exceptions) are to be managed:
These are the default settings in
<Errors> <Rule MatchFunction="*" MatchException="*" ReturnValue="#VALUE!" ShowMessage="true"/> </Errors>
This says for any function with any exception show the popup with an error message and then return
Pressing "Don't show again" will not show that error again during that session. If you want to permanently control how this error is shown you need to add to
<Rule MatchFunction="XPathOnUrl" MatchException="WebException" ReturnValue="" ShowMessage="false"/>
Rules are read and matched in order as they are written so put the default rule in the bottom.
If you want to have the error message returned in the result of the function: