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#1
It is mostly caused due to corrupt language packs. Can you uninstall all language packs, reboot the PC, and then try to install the service pack again?
Following on from my friend Dinesh's advice...
Some reading FYI.
windows 7 sp1 install 80073701 - Microsoft TechNet Search
Open the Windows Update troubleshooter
Error code 80073701 when downloading service pack 1 for windows 7. - Microsoft Answers
Troubleshoot problems installing Service Pack 1 (SP1) for Windows 7 and Windows Server 2008 R2