UPDATE:
Yes, it seems be a problem with permissions and Inspire. I set “755” to folder /my-project/system/expressionengine/third_party and all content, and after that the install process worked.
But I still have same permission problems. When loading the index page a lot of php errors and warnings appears, for example:
“Message: mkdir() [function.mkdir]: Permission denied
Filename: teemthumb/pi.teemthumb.php
Line Number: 456”
Obviously there are some chmod operations to perform…. My question now is: which permission settings should I use for each folder and file? Are there any documentation about this from EE’s point of view?