TYPO3 Core

TYPO3 version: 4.4.7
Powermail version: 1.5.7 with 'state' => 'excludeFromUpdates'

When in the extension manager, in the 'import' tab, I search for 'powermail'. I then get the following error:

t3lib_error_Exception

PHP Catchable Fatal Error: Argument 2 passed to t3lib_iconWorks::getSpriteIcon() must be an array, string given, called in /home/users/-x-/typo3/mod/tools/em/class.em_index.php on line 925 and defined in /home/users/-x-/t3lib/class.t3lib_iconworks.php line 640

When changing the state to 'stable' in the file 'ext_emconf.php' of 'powermail', the error is gone.