Even though Windows 2003 is going to be out of support in a few month, it still needs to be updated regularly. However, after patching cycle in February 2015 I could not get to update.microsoft.com. Well, actually I could, but the site showed the 0x80248015 error
You know that this is not easy to troubleshoot Windows Update issues. Same happened this time: I spent about an hour trying different advices and solutions, but could not fix it. Until have found this:
Thank you, Sanjay Sheth for your help!
The solution is really simple: you need to downgrade muweb.dll to version 7.6.7600.256.
The files are here (do not forget to extract them from .cab):
Copy 32-bit file to System32 on 32-bit Windows 2003 or to SysWOW64 on 64-bit Windows 2003
Copy 64-bit file to System32 on 64-bit Windows 2003
Simply close IE, replace the file(s) and start up IE again. No restart required!