unable to use EC2 service

[meirwah]

I'm using the lib for ec2 service.
For url :
https://ec2.eu-central-1.amazonaws.com/?ImageId=ami-9bf712f4&MaxCount=1&MinCount=0&Action=RunInstances

when I use the Sign() func, I get response 401 :

<?xml version="1.0" encoding="UTF-8"?>
<Response><Errors><Error><Code>AuthFailure</Code><Message>AWS was not able to validate the provided access credentials</Message></Error></Errors><RequestID>4bfd2d54-242d-4d4b-bfe5-768339e1559a</RequestID></Response>.

when I use the Sign4() func I get http response 500:

<?xml version="1.0" encoding="UTF-8"?>
<Response><Errors><Error><Code>InternalError</Code><Message>An internal error has occurred</Message></Error></Errors><RequestID>823256fe-0681-4578-862e-fa3458b84686</RequestID></Response>

Any idea?