Erratic .htaccess pattern

Hi list: I've just moved over alot of new information into a mysql database and am checking to see that members will be able to log in under the new system. I have a login page checking an htaccess file. The problem is, the htaccess file is only letting some of the members through, and denying access to others. I am just sitting here copy-pasting member usernames into a login box and watching while about 70% are accepted and the rest rejected. I can see no reason to the names that are reject: I can verify the table field is populated with the correct information (userid and passwd), and I am literally pasting the logins in -- so no chance of typos. I realize this is a vague statement -- but I can't seem to narrow any more specific data here. Here is the relevant text of the .htaccess file (i have 'blacked out' the protected info here with 'xxx'): AuthName "Authorization Required" AuthType Basic AuthGroupFile /dev/null AuthMySQLCryptedPasswords Off AuthMySQLHost localhost AuthMySQLDB xxx AuthMySQLUserTable Members AuthMySQLUser xxx AuthMySQLPassword xxx AuthMySQLNameField mem_user_id AuthMySQLPasswordField mem_passwd AuthMySQLAuthoritative On require valid-user Any thoughts? Thanks, Sarah