== What steps will reproduce the problem?
1. Create registry key (let's assume it's located in
HKEY_CURRENT_USER\TestKey);
2. Walk to it in "regedit";
3. Right-click on "(Default)" and select "Modify binary data";
4. Leave everything blank and press "OK";
5. Go to Python and execute this:
>>> import _winreg
>>> _winreg.QueryValue(_winreg.HKEY_CURRENT_USER, 'TestKey')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
SystemError: ..\Objects\stringobject.c:4271: bad argument to internal
function

== What is the expected output? What do you see instead?
I expect either returning "''" or some ValueError indicating that source
string is malformed.

== What version of the product are you using? On what operating system?
1. Windows XP Professional SP2 English;
2. Tested on Python 2.5.2;
3. Tested on Python 2.6.1;
4. Tested on Stackless Python 2.5.2.

== Please provide any additional information below.
And yes, I know that this function is lame and everybody using it also
is lame, but it's not really a reason to include buggy functions, right?

The attached patch will return "" in the case that Alex describes.
However, I haven't been able to reproduce his actions outside of
manually running the steps, so I don't have a test written for it.
Anyone know how to reproduce it from code?

I cannot reproduce this bug with the current 2.6.4 release - it is 
either fixed or masked now.

It happens to me on trunk with Windows XP. I also have access to Windows
Server 2003 where I can test this (haven't yet). Which version are you
running that you don't see this issue?

I've noticed this depends on the user privileges. When logged in as a 
normal user, I get the internal error as originally reported. When 
logged in as an administrator, there is no error and I get an empty 
string.