OBD System Checks "Fail"

[stanigu]

Hello

I went to have my '98 Boxster smogged here in California.

The car passed the actual emissions test, but it failed the "OBD System Checks". I did reset the OBD to clear some misfire codes, but I swear I've driven the car at least 1000 miles since doing so. My reader says that the car is ready for smog (i.e. it's gone through all the tests). Can anything else cause this error???

Thanks