Unable to add or change users Joomla 3.x AND 1.5 - Joomla! Forum - community, help and support

i'm reaching out in here because i've tried think of resolve this, , it's beyond limited brain. have 3 sites know of can no longer add new users or change password existing user via administration backend. well, matter can't change them frontend either. haven't tried going through database yet.

i first discovered issue on joomla 3.5 site, became apparent on joomla 1.5.x site (yes, know it's no longer supported), , discovered issue on joomla 3.6 site. here error message:

server error website encountered error while retrieving http://virtualcountrymall.com/administr ... =edit&id=0. may down maintenance or configured incorrectly. reload webpage. press reload button resubmit data needed load page.

i can add articles , make modifications modules, except dealing users. discovered when tried set user give template company access sites on unrelated matter.

i've asked hosting company, , tell me go forums, don't fix joomla issues. don't have extensions (that i'm aware of) on of these sites security akeeba admin tools. there cause issue?

any , appreciated.

if @ url posted, notice value of id zero. id points row in user table in database , value should not zero.

do have access mysql client application phpmyadmin cpanel can check condition of users table? alternatively, if hover cursor each user in name column, can check links, should unique , not end in zero.

if users table corrupted, there chance site has been compromised. can go 3.x security forum , check following sticky post do: viewtopic.php?f=714&t=757645