To reiterate, so all email has been deleted in PP and I'm assuming you have no emails at all listed in the PP "inbox" for this account since you've said you have "deleted all the emails in that account" that has the "1" count in the "unread" column with both "hide hidden messages" and "enable display filters" unchecked.
OK,
captJac we're going to try a few things if you don't mind (enumerated below)
with the "Enable display filters" unchecked.
Step 1) Do a
right/click on this specific account with the "1" count in the "unread" column and click on "
View Messages" (your account name will show here too).
Are
any messages listed in the inbox now at this time after doing the above

(you have said you've deleted all emails in this account so I'm just checking to see what this displays if anything after doing this).
So if no emails are displayed go to step 2.
Step 2) Do a
right/click on this specific account and click on "
Remove messages from list". You should now see that "1" count in the "unread" column change to "0". Now do a "
Mail check" on that specific account, that is
right/click on this specific account and click on "
Check Mail", does the "1" count in the "unread" column return
If the "1" count remains "0" and you still have no "messages" then we're done, problem solved skip remaining steps (but frankly, I don't expect this outcome unfortunately).
If the "1" count has returned after doing the "Mail check":
Do Step 1 again that you did before (see above), do you see
any messages for this account now
Step 3) If you still do not see any messages then try this
captJac, do a
right/click on this account with the "1" count in the "unread" column and click on "
Server info".
How many messages does this server info box say you have
Step 4) If it's not to much trouble while this server info box is displayed, would you please capture this (save this box) and post here in this topic when you can. You do this while this box is displayed by holding down the "
ALT" key + "
Prt Sc" key (at the same time) and then post this information here in this topic by replying and placing cursor in reply and
right/click and select
"Paste" to provide this information in your reply.
If you have any questions post back, thanks very much for the help
captJac.