Get file modified date in VB.NET

I have a number of files in a folder, and I need to get the last modified date. So I used

FDate = IO.File.GetLastWriteTime(FName)

It works fine with some files, but on others, I get a date of 1/1/1601. But when I check the files in Windows Explorer, all the dates look normal (recent). So, I'm guessing there are multiple file dates stored in the file system, and the ones .NET is seeing are not the ones Windows is seeing. How can I get exactly the date which appears as "date modified" in a file explorer window?

I tried some Visual Basic 6.0 API stuff, but that doesn't seem to work in .NET.