UnicodeEncodeError: 'ascii' codec can't encode character u'\xe4' in QGIS

Question

I am trying to perform a viewshed analysis in QGIS using a DSM raster file and a .shp file containing information on CCTV cameras. Example below:

Camera loc, Easting,    Northing,
Montpellier Station 359205  174540
Cheltenham Road, Station Road   358930  174586
Cheltenham Road, Zetland Road   358870  174734
Stapleton Road, Warwick Road    360634  174391
Rawnsley House, Lift #2 360341  173998
Rawnsley House, Main entrance (external)    360341  173998
Rawnsley House, Car park    360341  173998
Rawnsley House, Lift lobby  360341  173998
Rawnsley House, Left front (External PTZ)   360341  173998
Lower Ashley Road/Milpond Street    360375  174247
Wills Drive, Door panel 360409  173822
Twinnel House, Rear right (External PTZ)    360419  173813

Python, however, produces this error message:

Traceback (most recent call last):
              File "C:/Users/Lucas/.qgis2/python/plugins\ViewshedAnalysis\viewshedanalysis.py", line 161, in run
                outPath = ViewshedAnalysisDialog.returnOutputFile(self.dlg)
              File "C:/Users/Lucas/.qgis2/python/plugins\ViewshedAnalysis\viewshedanalysisdialog.py", line 60, in returnOutputFile
                return str(l)
            UnicodeEncodeError: 'ascii' codec can't encode character u'\xe4' in position 55: ordinal not in range(128)

I tried to solve the problem as Mickaël Bucas suggested. But since I have no clue about how to deal with python (I'm familiar with R though, if this helps) and don't know how transfer other solutions to my problem... can someone explain in a not-too-technical way how to solve this? I see that is has something to do with the encoding. The shp file is encoded in UTF-8. At least this was specified when I imported them to QGIS. Also I want to avoid import sys reload(sys) sys.setdefaultencoding("utf-8") (see this post)

Thanks!