If the username and password are specified, you need to have Bugzilla XML-RPC interface switched on. This is not required if you use anonymous access to Bugzilla without the username and password.
There are several known issues in Bugzilla regarding XMLs generated for the issues, which makes it hard to communicate with it. However, this can usually be fixed by tweaking the Bugzilla configuration.
If you see the path/to/bugzilla.dtd not found error, this means that the issue XML contains the relative path to the
bugzilla.dtdfile, and not the URL. To fix that, set the server URL in Bugzilla.
Sometimes you may see a
SAXParseExceptionsaying that Open quote is expected for attribute type_id associated with an element type flag. This happens because the generated XML does not correspond to the bundled
bugzilla.dtd. To fix it, make the
#IMPLIED(optional) in the bugzilla.dtd file. The issue and the workaround are described in detail here.