Hello.
At attempt online of update of system and applications the error began to arise.
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Fatal error: Cannot redeclare class JUpdaterSEF_Update in D:\www\stroystm\libraries\joomla\updater\adapters\sef_update.php on line 122
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It happens from for your component JoomSef
Installed version: 4.5.1.
Version Joomla - 2.5.19

Hi,

The reported file seems to be some left-over from older version of JoomSEF that wasn't deleted correctly during some previous update. You can safely delete the file D:\www\stroystm\libraries\joomla\updater\adapters\sef_update.php from your server. But of course, make a backup of your website before performing any such change to your files!