You can type invalid extension characters when you are creating or modifying a file association.

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The File Types tab in the Options dialog box does not validate the characters you type.

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Do not use spaces or special characters in an extension when you are creating or modifying a file association. Special characters you should not use in extensions include:

   <
   >
   |
   \ 
   / 
   :
   ;
   *
   ?
   "
				

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Microsoft is researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

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