I figured it out myself, piecing together information from a variety of threads.

To get the exact error, I used CPanel to look at the error logs for my site.  I found an entry like:

"/home/account_name/public_html/phplist/.htaccess: Invalid command 'php_value', perhaps mis-spelled or defined by a module not included in the server configuration"

To fix this error I did the following:

(1) First I created a php.ini file, which I saved in the phplist directory.  This file contained one entry

    magic_quotes_gpc = on

(2) Then I edited the .htaccess file in the same directory.  I found the line that was

    php_value magic_quotes_gpc on

and deleted it.  Then I added the line (I replaced 'username' with my account name)

    suPHP_ConfigPath /home/username/public_html

I was sort of feeling my way in the dark through this, so perhaps this solution is not complete, or not the most efficient.  But is works so far.

Cheers

Dave I