the install script will try to create the Connections/PowerStoreConnection.php file at the root of the PowerStore site.
This error can occur if the root does not allow read write permissions, or if the Connections folder is not created with read write permissions.
check to see if the Connections folder did get created. If it did, double check that is was created with read Worte permissions. If ot was not created, you will need to chmod the root of powerstore to allow read write. If it did get created, chmod the Connections folder to allow read write.