Script Tool Help! df = arcpy.mapping.ListDataFrames(mxd)[0] ISSUE

I'm trying to create a script tool but when I run the tool I keep getting and error message: I'm not sure what the problem is with
the df = arcpy.mapping.ListDataFrames(mxd)[0]

Traceback (most recent call last):
File "C:\Users\Courtney\Desktop\ScriptTool.py", line 14, in <module>
df = arcpy.mapping.ListDataFrames(mxd)[0]
File "c:\program files (x86)\arcgis\desktop10.1\arcpy\arcpy\utils.py", line 181, in fn_
return fn(*args, **kw)
File "c:\program files (x86)\arcgis\desktop10.1\arcpy\arcpy\mapping.py", line 1478, in ListDataFrames
result = mixins.MapDocumentMixin(map_document).listDataFrames(wildcard)
File "c:\program files (x86)\arcgis\desktop10.1\arcpy\arcpy\arcobjects\mixins.py", line 727, in listDataFrames
return list(reversed(list(self.dataFrames)))
File "c:\program files (x86)\arcgis\desktop10.1\arcpy\arcpy\arcobjects\mixins.py", line 694, in dataFrames
return map(convertArcObjectToPythonObject, self.pageLayout.dataFrames)
File "c:\program files (x86)\arcgis\desktop10.1\arcpy\arcpy\arcobjects\mixins.py", line 678, in pageLayout
return convertArcObjectToPythonObject(self._mxd._arc_object.pageLayout)
AttributeError: 'unicode' object has no attribute '_arc_object'

Failed to execute (ScriptTool).


MY SCRIPT IS AS FOLLOWS:

#Import Modules
import arcpy
from arcpy import env
import datetime
import os

arcpy.env.overwriteOutput = True

#Define Variables
mxd = arcpy.mapping.MapDocument = arcpy.GetParameterAsText(0)
env.workspace = arcpy.GetParameterAsText(1)
df = arcpy.mapping.ListDataFrames(mxd)[0]



#Define variables
featureClass = arcpy.GetParameterAsText(2)
layer = "AISlayer" #layer Name
OutlyrFile = r"C:\Courtney\Jan1AIS.lyr"
addLayer = arcpy.mapping.Layer(OutlyrFile)

#Make a layer from the feature class
arcpy.MakeFeatureLayer_management(featureClass , layer) #This creates a temporary layer in memory
#Save the layer in memory to layer
arcpy.SaveToLayerFile_management(layer, OutlyrFile) #This saves the layer to the disk

#Check to see if layer supports time and if time properties are set
lyr = addLayer
if lyr.supports("TIME"):
lyrTime = lyr.time
if lyr.time.isTimeEnabled:
LYRstartTime = lyrTime.startTime
LYRendTime = lyrTime.endTime
timeDelta = LYRendTime - LYRstartTime
print "Start Time: " + str(LYRstartTime)
print "End Time: " + str(LYRendTime)
print "Time Extent: " + str(timeDelta)
else:
print "No time properties have been set on the layer"
#Enables time on a layer with another already time enabled layer
#Do this within the else statement because you only want to enable time if it isn't already
#df = arcpy.mapping.ListDataFrames(mxd)[0]
#lyr = arcpy.mapping.ListLayers(mxd, "Jan1AIS", df)[0]
timeFile = arcpy.mapping.Layer(r"C:\Courtney\TimeLayer.lyr") #originally authored in ArcMap
arcpy.mapping.UpdateLayerTime(df, lyr, timeFile) #refrence in toolbox, SAVE ZIP, navigate to file
print "Time has been enabled."
else:
print "Time is not supported on this layer"

#Add layer to the data frame
arcpy.mapping.AddLayer(df, addLayer)
#Save the mxd
#mxd.save()


lyr = arcpy.mapping.ListLayers(mxd, layer, df)[0]
for df in arcpy.mapping.ListDataFrames(mxd):
#zoom to to the extent of the selected features for a specific layer
df.extent = lyr.getSelectedExtent()
#Set mape scale...each data frame's rotation property to 0 and scale property to 1:20,000,000
df.rotation = arcpy.GetParameterAsText(3) #0
df.scale = arcpy.GetParameterAsText(4) #20000000
mxd.activeView = 'PAGE_LAYOUT'

inFolder = arcpy.GetParameterAsText(5)


df.time.currentTime = arcpy.GetParameterAsText(6) #datetime.datetime(2009, 01, 1, 00, 00)
endTime = arcpy.GetParameterAsText(7) #datetime.datetime(2009, 01, 1, 23, 59)
interval = arcpy.GetParameterAsText(8) #arcpy.time.EsriTimeDelta(1, 'hours')
#or #interval = datetime.timedelta(hours=1)