[GRASS-user] GRASS r.flow command error

[john polo]

Hi,
I am using the r.flow command from the GRASS toolset inside of QGIS with
no success. My apologies if this should be on QGIS-users instead. The
raster file I am using is an elevation map from USDA's data gateway. I'm
on a Win 7 64bit machine with QGIS 2.4 just recently installed.

In the first window of r.flow there are dropdown menus for Elevation,
Aspect and Barrier data. The manual says the aspect and barrier maps are
optional, but there is no way to leave those selections blank. At first,
I was using the same elevation map in all the dropdown options. Then I
used the aspect command to create an aspect map. I don't know how to
make the barrier map, so I left the elevation map.

So I've tried the command several times and I keep getting a window
titled "Problem loading output layers" that lays over the main r.flow
window. The Problem window goes on to say that the flowline, flowpath,
and flowline density layers can not be found. The window includes a
message about checking the log. The window concludes, saying that GRASS
appears to be correctly installed.

If I click on "close" or the X in the corner of the Problem window, it
closes the r.flow window too, before I can search the r.flow log tab. I
can't just select the r.flow window while the Problem window is open,
the r.flow window is frozen/grayed out, so I need to close the Problem
window to get back to the r.flow, but the r.flow window closes with the
Problem window, so I get nowhere as far as reading the log.

If I read the message panel it says "Data source invalid ()". I don't
know if this the terse version of the r.flow log or what. Any help will
be appreciated.

John