Problems synchronizing with gmail

hi,
since yesterday, i have problems syncing with gmail.
i receive all the gmail emails without none problem,
and the emails are correctly readed (on my android).
but when i receive another email, all previously received
emails are marked unread (another time), even if i
delete (on my android).
i mark read, or delete, or delete the "received" label
from emails, but the next time i receive a email, it's
marked unread
if i access to my gmail account via pc and i mark as
read, or deleted, the mails are correctly processed and
the next time i receive a email are not marked unread at
phone.
my gmail config are unchanged since a month...
ideas ?

Try this
Settings - Applications - Manage Applications - Menu:Filter "All"
GMAil - Clear data
GMail Storage - Clear data

solved!!!
i agree to you very much!!!