I'm not sure that it's the size of your header that is the problem. I'd be interested more in what you are trying to do when you get this error message. Looking up that error message, it seems to be from the dcerpc package, so I'm guessing that it might be the dcom exploit but if you can tell us the commands that you ran within metasploit to get the error, then we can maybe help you troubleshoot the problem better.
Well i m using a GUI metasploit in which :
1. selected exploit/windows/dcerpc/ms03_026_dcom
2. Target is my laptop which has xp sp 2
3. payload used is Windows/shell_reverse_tcp
4. rhost is set to laptop IP
after i apply the exploit i m getting:-
22:07:55 - ms03_026_dcom
- Launching exploit windows/dcerpc/ms03_026_dcom...
22:07:56 - ms03_026_dcom
22:07:56 - ms03_026_dcom
- Trying target Windows NT SP3-6a/2000/XP/2003 Universal...
22:07:56 - ms03_026_dcom
- Binding to 4d9f4ab8-7d1c-11cf-861e-0020af6e7c57:0.0@ncacn_ip_tcp:192.168.2.1[135] ...
22:07:56 - ms03_026_dcom [-] Exploit failed: Invalid packet. Packet header must be at least 10 bytes long
My pc has xp sp 2..