[Qgis-user] GRASS r.flow command error

[john polo]

Hi,
I recently posted this to the GRASS-users list and was informed this 
list is more appropriate, sorry for cross-post. I am using the r.flow 
command from the GRASS toolset inside of QGIS with no success. The 
raster file I am using is an elevation map from USDA's data gateway. 
It's actually a clip from the original DEM. 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. I have tried the r.drain command with similar outcomes.

John