Hi,
It would appear that the 'Restrict Extension' option for FileSelectPopupEx(...) is case sensitive. Or in other words if I restrict the extension to "*.txt" and I try to open a file with an extension of ".TXT", it won't let me, telling me that I'm restricted to ".txt". From my understanding the NI function is just a wrapper around the Windows API so I'm not sure what can be done about this but I thought I might point it out.