I had the same issue as you some months ago.
I tried all the usual suggestions (see above) but they did not work for me and my W7 OS.
What did work for me was this freeware:
Free ANSI PST to Unicode PST software, Convert ANSI PST to Unicode PST, Convert Unicode PST to ANSI PST
P.S. Make a copy of the pst file before you start converting the original so that at least you have something to go back to if all else fails.
Good luck.