Error messages on Users and Roles and Admin

Hi all, Some help would be appreciated with these error messages. I’m not a techie so some advise on how to fix this problem would be mich appreciated. Thanks.

When I click on Users and Roles I get this error message:

Fatal error: Uncaught Error: Undefined class constant ‘FORM_NOTIFY_USERS’ in /home/murmur/public_html/ojs/lib/pkp/pages/management/ManagementHandler.inc.php:393 Stack trace: #0 /home/murmur/public_html/ojs/lib/pkp/pages/management/ManagementHandler.inc.php(78): ManagementHandler->access(Array, Object(Request)) #1 /home/murmur/public_html/ojs/lib/pkp/classes/core/PKPRouter.inc.php(395): ManagementHandler->settings(Array, Object(Request)) #2 /home/murmur/public_html/ojs/lib/pkp/classes/core/PKPPageRouter.inc.php(246): PKPRouter->_authorizeInitializeAndCallRequest(Array, Object(Request), Array, false) #3 /home/murmur/public_html/ojs/lib/pkp/classes/core/Dispatcher.inc.php(144): PKPPageRouter->route(Object(Request)) #4 /home/murmur/public_html/ojs/lib/pkp/classes/core/PKPApplication.inc.php(362): Dispatcher->dispatch(Object(Request)) #5 /home/murmur/public_html/ojs/index.php(68): PKPApplication->execute() #6 {main} thrown in /home/murmur/public_html/ojs/lib/pkp/pages/management/ManagementHandler.inc.php on line 393

When I click on something in Admin, I get this message:

Fatal error: Uncaught GuzzleHttp\Exception\RequestException: cURL error 56: Recv failure: Connection reset by peer (see https://curl.haxx.se/libcurl/c/libcurl-errors.html) in /home/murmur/public_html/ojs/lib/pkp/lib/vendor/guzzlehttp/guzzle/src/Handler/CurlFactory.php:201 Stack trace: #0 /home/murmur/public_html/ojs/lib/pkp/lib/vendor/guzzlehttp/guzzle/src/Handler/CurlFactory.php(155): GuzzleHttp\Handler\CurlFactory::createRejection(Object(GuzzleHttp\Handler\EasyHandle), Array) #1 /home/murmur/public_html/ojs/lib/pkp/lib/vendor/guzzlehttp/guzzle/src/Handler/CurlFactory.php(105): GuzzleHttp\Handler\CurlFactory::finishError(Object(GuzzleHttp\Handler\CurlHandler), Object(GuzzleHttp\Handler\EasyHandle), Object(GuzzleHttp\Handler\CurlFactory)) #2 /home/murmur/public_html/ojs/lib/pkp/lib/vendor/guzzlehttp/guzzle/src/Handler/CurlHandler.php(43): GuzzleHttp\Handler\CurlFactory::finish(Object(GuzzleHttp\Handler\CurlHandler), Object(GuzzleHttp\Handler\EasyHandle), Object(GuzzleHttp\Handler\CurlFactory)) #3 /home/murmur/public_html/ in /home/murmur/public_html/ojs/lib/pkp/lib/vendor/guzzlehttp/guzzle/src/Handler/CurlFactory.php on line 201