Mail stopped working on iPad & iPhone, but not G5, after installing iOS 7.

Question

Here we have a G5, an iPhone-4 and an iPad all linked to the same POP account.  Mail fetching on all three devices had been working fine. 
Earlier this week (10/23 or 10/24), however, Mail on both the iPhone and the iPad quit working shortly after our having installed iOS 7 on each of them.   This could be a coincidence, but Mail on a G5 running 10.5.8 linked to the same account is still fetching and sending mail just fine.
Every time we swipe down on the message list (the gesture to fetch new mail) in Mail on the iPad, an error message appears,
Cannot Get Mail
The user name or password for
"Primary Mail Account" is incorrect
Settings   |    OK
An analogous gesture on the iPhone produces the same message.
But Mail on the G5 (running 10.5.8) still works fine to fetch mail from the same POP account.
Here are some details:
About two weeks ago, we installed iOS 7 on the iPad and the iPhone.  Mail continued to work after the installation.
About a week later, last Wednesday, 10/23, the iPad went through a spontaneous installation event, in which the multilingual series of "Hello!" images familiar to those who install Mac operating systems floated across the screen.  Apparently, this event installed iOS 7.0.3.  There followed a short series of initialization dialogs, then everything seemed to work OK.
Except that Mail wasn't working.  This could be a coincidence, but Mail on this iPad has not worked since last Wednesday.  The last message received is dated last Wednesday.
We don't know whether the iPhone went through a similar event, but Mail quit working on it, as well.  Mail on this iPhone now gets the same message, above, as on the iPad.  The last message received by the iPhone was last Thursday, 10/24.  The iPhone's iOS is now 7.0.2.  The iPhone says that iOS 7.0.3 is downloaded, but not yet installed. 
We compared the settings for Mail on the G5, on which Mail is still working, against the settings on the iPad and the iPhone.  They all seem pretty much the same.
Have you heard of anyone else with this problem, or might you have an idea how to research it?
--Gil

Answer 1

That worked!  A couple of notes for anyone with the same problem:
I thought I'd be clever and create a new account before deleting the old one.  That didn't work, as "Settings" kept insisting that the account had already been created.  I had actually to delete the old account and create a new one from nada.
I was careful to write down all the settings parameters first.  Even so, it took a few tries to get everything spelled right.  Fortunately, "Settings" checked everything carefully and its messages pointed to the right places.
I still got the same error message the first time i relaunched Mail.  However, this time I chose the "OK" option.  Since then and thereafter it seems to be working.
Thanks for your help, lizdance40.
--Gil