---
title: "TYPO3 Exception 1166546734"
manual: "TYPO3 Exceptions"
version: "main"
permalink: "https://docs.typo3.org/permalink/t3exceptions:typo3-exception-1166546734"
source: "Exceptions/1166546734.rst"
modified: "2026-09-16T07:39:08+00:00"
---

# TYPO3 Exception 1166546734

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## #1166546734 TYPO3CMSCorePackageExceptionUnknownPackageException

### Reason 1:

-   Package does really not exist

### Reason 2:

|Extension Upload screen TER.png|

-   CamelCaseConversion Problem with numbers
-   f.e. vendor_extension_2018 will be converted into VendorExtension2018
    and converted back into vendor_extension2018

This will result in the following error message:

> Package "vendor_extension2018" is not available. Please check if the
> package exists and that the package key is correct (package keys are
> case sensitive)

According to the hints in TER these kind of keys are invalid:

-   [https://docs.typo3.org/typo3cms/CoreApiReference/ExtensionArchitecture/ExtensionKey/Index.html](https://docs.typo3.org/typo3cms/CoreApiReference/ExtensionArchitecture/ExtensionKey/Index.html)

### Reason 3:

> 1/1) #1166546734 TYPO3CMSCorePackageExceptionUnknownPackageException
> Package "" is not available. Please check if the package exists and that the package key is correct (package keys are case sensitive).

Happened on switching from LTS 9 to 10 as `$_EXTKEY` is no longer defined. Therefore I called:

```
\TYPO3\CMS\Extbase\Utility\ExtensionUtility::registerPlugin(
     'VENDOR.' . $extensionKey,
     'Pi1',
     'LLL:EXT:...'
 );

```

With an empty `$extensionKey`

### See also

-   [https://forge.typo3.org/issues/87737](https://forge.typo3.org/issues/87737)