Pinned files cannot be directly checked out and modified. You will have to
branch the pinned file into a new project before you can change it. Pinned
files usually represent an older version of a file, and if you were allowed
to directly modify it, you would alter the change history, preventing
versions newer than that from being retrieved. SourceSafe does not store
the entire version of text file, only the change history so that earlier
versions can be 'rebuilt'.

Chris Cooper
Microsoft

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