Can't open source-files from Project Manager under Windows 7

Have a simple project consisting of one master.qbs and a test.qbs two directory levels below.
While I'm able to open the .qps files I'm not able to open the main.c which is shown on the left.
The file exists and the project compiles fine.

Attached a screenshot of the error message

— master.qbs —
import qbs.base 1.0
Project {
references: [
"test/test1/child.qbs"
]
}

— test/test1/child.qbs
import qbs.base 1.0
Application {
name: "Test"
files: ["main.c"]
Depends

}