need help debugging my email in squeeze and/or testing (both) not merely old squeeze from before the release

Some background information:

I have used mutt/fetchmail/exim4 for several years without much problem. I keep backup copies of /etc so I am confident that my exim4 configuration is the same as it was when
it last worked a few days ago. I have looked at the config file that is causing a problem and it is correctly formatted (i.e. not corrupted by garbage and contining information which
works in other contexts) But for reasons that are too complex to go into, I got my computer into a state where I needed to re-install Squeeze from scratch. And ...
now exim4 is unable to send email to the SMTP server that I use. It is not something outside at my ISP because the exim4 scripts (or whatever) leave a paniclog message in
/var/log/exim4, which reads as follows:

2011-02-27 09:04:28 1Ptj6i-0004BD-8e failed to expand "<; ${if exists{/etc/exim4/passwd.client} {${lookup{$host}nwildlsearch{/etc/exim4/passwd.client}{$host_address}}}{} }" while checking a list: failed to open /etc/exim4/passwd.client for linear search: Permission denied (euid=102 egid=104)
2011-02-27 10:56:51 1PtkrT-0000gF-5a failed to expand "<; ${if exists{/etc/exim4/passwd.client} {${lookup{$host}nwildlsearch{/etc/exim4/passwd.client}{$host_address}}}{} }" while checking a list: failed to open /etc/exim4/passwd.client for linear search: Permission denied (euid=102 egid=104)

I look at the file, /etc/exim4/passwd.client, and it contains exactly the same bytes as it has always contained since many months ago when I first got the setup working. It contains
one line that is not a comment, and immediately above is a comment that specifies the required format. These are:

### target.mail.server.example:login:password
smtp.everyone.net:pecondon@mesanetworks.net:----------- (note: my password is not actually a bunch of hyphens ;-)

(except that I haven't revealed the actual password, But I know that password is good because I am using the web connection to my ISP to write this email and I used the same
password to log on to the web mail. And anyway, the error message is about being unable to parse the content of this file, not that it is an incorrect password.)

I also tried installing the current testing (Wheezy) and found the same problem. The behavior of the reinstalled system indicate to me that although I was frequently upgrading
while squeeze was still testing, the many packages were not, in fact, being kept in sync with the repository, i.e. a persistent cryptic (hidden) problem in aptitude. But for now
I'd just like to get email working again.

I am able to receive email. The same password continues to work in the fetchmailrc. Please help.

Paul
pecondon@mesanetworks.net