Can't Clear Maintenance Reminder

I am working with a r2000ic fanuc with a r30ib A-cabinet.
I get a maintenance reminder about the 1st. cleaning of cont. ventilation. At first sight it's all ok with that. I try to process it done by clicking complete -> Yes but nothing happens. I have tried with other reminders and it works, but with that one no. Do you have any idea or clue about whats happening? Tank you so much in advance.