Try urlencoding each querystring parameter:
customerUserAgent=Mozilla/5.0 (Windows NT 6.1) AppleWebKit/535.11 (KHTML, like Gecko) Chrome/17.0.963.83 Safari/535.11
arrivalDate=12/10/2012
The customerUserAgent url param should be url encoded:
customerUserAgent=Mozilla%2F5.0%20(Windows%20NT%206.1)%20AppleWebKit%2F535.11%20(KHTML%2C%20like%20Gecko)%20Chrome%2F17.0.963.83%20Safari%2F535.11
arrivalDate=12%2F10%2F2012
Take a look at PHP's urlencode for more information.
Also, be sure to remove the spaces between each querystring param, not sure if it was copy/paste issue or not.
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