You’ll need to be much more specific for anyone to help you. 🙂
Ok… in file bp-core-functions.php (line 640) system tries to calculate how old is a activity listed. a variable called $seconds seems to be 0 or not a number… so division is illegal and system show how old is the post in seconds… and not in years, months, days, hours, minutes…
It happens since I’ve updated be to 1.8…
I’ve edited default-constants.php from wp-admin to remove all spaces in YEAR_IN_SECONDS and other constants could be used by bp-core-functions.php… so this is not the problem