mark
it seems to be a problem with a door or window frame . . . someone with the US special edition library will be able to track it down further. but a quick check could be to ensure that you haven't set any zero or minus values for any of the doors or windows that appear in that section/elevation.
you can turn off the 'annoyance' in your work environment: go to User Preferences>Imaging and Calculation> and uncheck 'interrupt with error messages'.
HTH
~/archiben
b e n f r o s t
b f [a t ] p l a n b a r c h i t e c t u r e [d o t] n z
archicad | sketchup! | coffeecup