panic when parsing xml

I'm new to mosync and app development. I would like to use the xml parser to extract some information (a list of users) from a web page that I download using a http connection. When I try to parse the data the app crashes (in an android 2.0 emulator) with panic code 40035.

Here is my parser:

class UserListParser :
	private Mtx::XmlListener,
	private Mtx::MtxListener
{
public:
	void parse(MAUtil::String& tagdata);

private:

	// for test purposes (I derive a screen from UserListParser that implements
	// someEvent() and have it display a debug message)
	virtual void someEvent(MAUtil::String stuff) = 0;

	// from XmlListener
	void mtxEncoding(const char* value);
	void mtxTagStart(const char* name, int len);
	void mtxTagAttr(const char* attrName, const char* attrValue);
	void mtxTagStartEnd();
	void mtxTagData(const char* data, int len);
	void mtxTagEnd(const char* name, int len);
	void mtxParseError(int offset);
	void mtxEmptyTagEnd();
	unsigned char mtxUnicodeCharacter(int unicode);

	// from MtxListener
	void mtxDataRemains(const char* data, int len);

	// private members
	MAUtil::String tagdata;
	Mtx::Context parser;
};

here is the implementation of the only public method:

void UserListParser::parse(MAUtil::String& tagdata)
{
	// copy the data
	UserListParser::tagdata = tagdata;

	// start parsing, here is where it crashes
	parser.feed(tagdata.pointer());

	// the following line is not executed
	someEvent("not crashed... yet");
}

here is what happens in the screen (which is derived from UserListParser):

void TextScreen::someEvent(MAUtil::String stuff)
{
	addText(stuff);
}

void TextScreen::addText(const MAUtil::String& str)
{
	 MAUtil::String text = mainLabel->getText();
	 text.append("\n", 1);
	 text.append(str.c_str(), str.length());
	 mainLabel->setText(text);
}

I imagine it is maybe a problem with the string handling.

Is the char* data returned by String::pointer() zero-terminated? What is the difference between pointer() and c_str()?

What could I possibly be doing wrong? Thanks for any help with this.

I hope I'm in the right section of the forum with this question.