I'm trying to create a virtual raster in QGIS 2.6.1 64b on Windows, but I get the message:

> 
> "The process failed to start. Either the invoked program is missing,
>  or you may have insufficient permissions to invoke the program."
> 
> 
> 

I try to read in a whole directory, selecting also to "Recurse subdirectories"
it works for a part of my datasets, but not for all.
I thought it is related to the the size of the datasets, so I tried dividing the bigger datasets in smaller directories. but it did not work.