Exchange 2010 Export of PST with Date Range
You need a few parentheses to make the ContentFilter logic stick. Try this:
{((Received -lt ’04/01/2010′) -and (Received -ge ’03/01/2010′)) -or ((Sent -lt ’04/01/2010′) -and (Sent -ge ’03/01/2010′))}
Edit: I think actually you should use double quotes for the dates in stead of single quotes. It might not matter, but if the above doesn't work, try substituting the single quotes with doubles