When accessing an aspx page on a Motorola Droid using the default browser I get the error:
error on line 1 at column 1: Document is empty.
 
This even happens on a simple page that does nothing more than response.write("hi")
Pages that are more complex get other errors, but this seemed to be the simplest way to have a recreation scenario for you. The same page can be accessed by other mobile devices and by desktop browsers with no errors.
 
The isMobileDevice does equal true, so it is being recognized. This error happens with the latest version (2010-04-16) and the first occurrence of the error is with the 2010-02-10 release of the mobile browser file where the Droid was first recognized as a mobile device.
 
The http headers are:
Accept: application/xml,application/xhtml+xml,text/html;q=0.9,text/ plain;q=0.8,image/png,*/*;q=0.5
User-Agent: Mozilla/5.0 (Linux; U; Android 2.1-update1; en-us; Droid Build/ESE81) AppleWebKit/530.17 (KHTML, like Gecko) Build/ESE81) AppleWebKit/530.17 (KHTML, like Gecko) Version/4.0 Mobile Safari/530.17
 
Accept-Charset: utf-8, iso-8859-1, utf-16, *;q=0.7 NB:
 
Please let me know if there is anything else I can do to help. Thanks!