> I use the File -> Write File Action to do it.
> Any ideas what is the problem? Is it a bug in Tasker?
If the file is written as requested by the action, it's not likely a
bug in Tasker.
Maybe dropbox is registed for a 'file created' signal from the OS
rather than
a 'file modified' (which is what Tasker is doing, just adding a line).
In which
case you could write to another file somewhere instead and then copy
it across to the dropbox folder with Tasker.
Alternatively try an SD card scan to get the OSs attention ?
(Tasker media category I think)
Pent