Earlier versions of Word blocked by SP3

Since downloading Service Pack 3 update i am not able to open some old files created in Word 2003. I am getting an error message saying

"You are attempting to open a file that was created in an earlier version of Microsoft Office. This file type is blocked from opening in this version by your registry policy setting."

I am not able to make out what went wrong with the update, Is there anything i can try out for getting access to those files. I did not had any such issue before installing the update.

You can go through below article and try out the solution mentioned for dealing with that error:
You receive an error message when you try to open a file type that was blocked by your registry policy settings in Word 2010, in Word 2007, or in Word 2003
If at all you don't get any help from the solution that have been mentioned there then you can try using below .reg files for changing security settings:
To restore the blocked Word file types only - RestoreBlockingWord.reg