TYPO3 Core

In the extension-manager on the updtae-tab I get the following message shown:

Update Extension List
parsererror(SyntaxError: Unexpected token < in JSON at position 0): <script type="text/javascript">
/*<![CDATA[*/
    (function debug() {
        var message = 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v\u0020class=\u0022extbase-debugger\u0020extbase-debugger-inline\u0022\u003E\u000A\u0009\u0009\u0009\u0009\u003Cdiv\u0020class=\u0022extbase-debugger-top\u0022\u003E\u003C\/div\u003E\u000A\u0009\u0009\u0009\u0009\u003Cdiv\u0020class=\u0022extbase-debugger-center\u0022\u003E\u000A\u0009\u0009\u0009\u0009\u0009\u003Cpre\u0020dir=\u0022ltr\u0022\u003E\u0027\u003Cspan\u0020class=\u0022extbase-debug-string\u0022\u003EUsage\u0020of\u0020client\u0020related\u0020conditions\u0020(browser,\u0020device,\u0020version,\u0020system,\u0020userag\u003Cbr\u0020\/\u003E\u0026nbsp;\u0026nbsp;\u0026nbsp;ent)\u0020is\u0020deprecated\u0020since\u00207.0.\u003C\/span\u003E\u0027\u0020(105\u0020chars)\u003C\/pre\u003E\u000A\u0009\u0009\u0009\u0009\u003C\/div\u003E\u000A\u0009\u0009\u0009\u003C\/div\u003E',
            messagePlain = '\u000A\u0022Usage\u0020of\u0020client\u0020related\u0020conditions\u0020(browser,\u0020device,\u0020version,\u0020system,\u0020userag\u000A\u0020\u0020\u0020ent)\u0020is\u0020deprecated\u0020since\u00207.0.\u0022\u0020(105\u0020chars)',
            header = '02-02-17\u002007:24:\u0020',
            group = 'Deprecation\u0020Log';
        if (top.TYPO3 && top.TYPO3.DebugConsole) {
            top.TYPO3.DebugConsole.add(message, header, group);
        } else {
            var consoleMessage = [group, header, messagePlain].join(" | ");
            if (typeof console === "object" && typeof console.log === "function") {
                console.log(consoleMessage);
            }
        };
    })();

/*]]>*/
</script><br />
<b>Fatal error</b>:  Call to a member function getUid() on

In the bottom the message seems being cropped, but that seems being the important part.
Server-logs are not accessible.
The update of the extensions is not done.
This happens in several sessions and browsers.

In the module System->Log the following message is shown:

Core: Exception handler (WEB): Uncaught TYPO3 Exception: #1417988921: The CSRF protection token for the requested module is missing or invalid | TYPO3\CMS\Core\Exception thrown in file /.../typo3/sysext/backend/Classes/Http/BackendModuleRequestHandler.php in line 82. Requested URL: http://.../typo3/index.php?M=tools_ExtensionmanagerExtensionmanag%E2%80%A6er_tools_extensionmanagerextensionmanager%5Bformat%5D=json&_=1486015893952