Different solution to date field question mark
*EDIT: THIS FIRST POST DOES NOT RESOLVE THE PROBLEM. SEE POSTS AFTER THIS. [I'm only leaving this post in case someone wants to try any of the steps mentioned in the replies]*
Ever since I had updated to FMPro 11, I've had trouble with the date fields in my forms displaying a question mark. If I clicked in the field, the current date would display, which was what it was supposed to do—automatically enter. But once I tabbed out of the field, it reverted back to a question mark. Also, during that period when the date did show, the slash mark separators in the date were missing. I took this as a clue and tried all sorts of things from changing date formats to fonts. I tried changing the size of the field in case it was too small to display the date (though it had always been fine in previous versions). I deleted it and put the field in again. Nothing ever worked.
Today I found the solution. I tried to check the definition of the field. Everything was fine. Then it occurred to me that maybe there was a duplicate date field and I might be using the wrong one, or it was conflicting somehow.
My date field—that I'd been using for years, through at least 6 or 7 versions—was called "Invoice Date." I scrolled through the list of fields and came to one at the bottom that I didn't recognize: "Today." I never created that field. In the Comment for it, it said "Generated by conversion." All I can think is that when the files were converted for the new version, it generated the "Today" field, and no longer recognized the old "Invoice Date" field. When I looked at the options, it had the same options as my old field, so I tried it. I replaced the Invoice Date field with the Today field, and now it fills in correctly and stays entered now.
This should be considered a bug, and it's caused me many hours of frustration trying to fix it. An update and the subsequent file conversions should not be messing with your user-defined fields. Nowhere in my searches for a solution for this over a long time has this ever come up as a reason. Maybe my case is unique, but just in case it isn't, I want to let people know to look for this.