Currently it does not appear to be possible to copy error messages from the Inline Function log, this would be very useful when having to Google compiler errors and such, or pasting to the forum.
Because log messages get cut off after ±259 characters, this doesn't always allow reading of the full error message.
The main window's log has a tooltip to display the full message, which would work here as well.
EDIT: Feature was added; Thanks, Gary!