TypeError: cannot concatenate 'str' and 'int' objects

[zbayarea]

I'm sending about 1 mil. emails per day and I am getting about 250K erros like this
ms=22 cpu_ms=0 api_cpu_ms=0 cpm_usd=0.003879
E 2011-03-10 07:13:36.775
cannot concatenate 'str' and 'int' objects
Traceback (most recent call last):
File "/base/python_runtime/python_lib/versions/1/google/appengine/ext/webapp/init.py", line 517, in call
handler.post(*groups)
File "/base/data/home/apps/bloog444/1.348886030884843708/main.py", line 135, in post
self.response.out.write("Success")
File "/base/python_runtime/python_dist/lib/python2.5/contextlib.py", line 33, in exit
self.gen.throw(type, value, traceback)
File "/base/data/home/apps/bloog44/1.348886030884843708/main.py", line 72, in mailExcpHandler
xml_error_response(ctx, 500 ,'system.other', 'An unexpected error in the web service has happened: ' + exc.message)
TypeError: cannot concatenate 'str' and 'int' objects