Upgrade From 4.0.3 To 4.1.1 Falied (Windows Server)

Good morning.

I have tried to upgrade a local copy of our e-shop which i backed up and restored in a windows installation with Apache 2.4 and PHP 5.6.17.

We wanted to test the upgrade process on a local server before proceeding to our live e-shop.

When i clicked Upgrade on the Upgrade center i received the following error message:

Warning: simplexml_load_file(): I/O warning : failed to load external entity "C:/Apache24/htdocs/mytentag/var/upgrade/upgrade_4.0.3_ultimate-4.1.1_ultimate.tgz/uc.xml" in C:\Apache24\htdocs\mytentag\app\controllers\backend\upgrade_center.php on line 178

I have also noticed that the file uc.xml does not exist in the folder C:\Apache24\htdocs\mytentag\var\upgrade\upgrade_4.0.3_ultimate-4.1.1_ultimate.tgz

Can somebody help me?

I have searched the net but didnt find anything for a windows server installation.

Thank you in advance