Python script and Firefox add-on Postor HTTP post sending NULL values | ThingSpeak API | Forum

I have created a new channel with only one field and have tried to post the field data using both python script from a raspberry PI and a direct post using the firefox addon POSTOR. the data was posted as NULL when i checked the JSON. What am i doing wrong? Please see my script also below.

# Return CPU temperature as a character string
#!/usr/bin/python
import os
import httplib, urllib
import time

def getCPUtemperature():
res = os.popen('vcgencmd measure_temp').readline()
return(res.replace("temp=","").replace("'C\n",""))

def postStats():
cpuTemp1 = getCPUtemperature();

print "CPU Temp: ", cpuTemp1

params = urllib.urlencode({'cputmp': cpuTemp1,'key':'XXXXXXXXXXXXX'})
headers = {"Content-type": "application/x-www-form-urlencoded","Accept": "text/plain"}
conn = httplib.HTTPConnection("api.thingspeak.com:80")
conn.request("POST", "/update", params, headers)
response = conn.getresponse()
print response.status, response.reason
data = response.read()
conn.close()

if __name__ == "__main__":
while True:
postStats()
time.sleep(30)