You're trying to set the path up incorrectly. What you need to do is
delete the Path property node and the reference control connected to
it, then right click on the Path terminal of the Write to
Spreadsheet.vi and create a control. The Control you currently have is
a reference value to a non existant path control.
As for the tunnel error, since you are only writing values in the one
case, just move the Write to Spreadsheet.vi and it's new control inside
the Readings case. If you leave it where it is, you'll get a file
writting everytime the VI runs, even if there's no readings to record.
If you did want it to run everytime, then would need to wire something
to the tunnel from each case of the Case Structure so it has values to
write.
Ed

Ed Dickens - Certified LabVIEW Architect
Lockheed Martin Space
Using the Abort button to stop your VI is like using a tree to stop your car. It works, but there may be consequences.