Is there a "nuclear option" for closing/freeing a file?

Question

My original related question here (https://stackoverflow.com/questions/17332403/is-there-such-a-c-sharp-method-or-methodology-that-would-equate-to-filealready) was marked as a duplicate, and I used the supposed duplicate (Is there a way to check if a file is in use?) to try to solve my problem, but I'm still getting flooded with Null Reference Exceptions on some file I/O operations.

Based on that halcyon post of yore, I altered the previous code from this:

public FileQuickRead(string filename)
{
    try
    {
        SR = File.OpenText(filename);
    }
    catch (Exception ex)
    {
        CCR.ExceptionHandler(ex, "FileQuickRead.FileQuickRead");
    }
    . . .

...to this:

public FileQuickRead(string filename)
{
    // Added 6/27/2013; adapted from https://stackoverflow.com/questions/876473/is-there-a-way-to-check-if-a-file-is-in-use
    try
    {
        using (Stream stream = new FileStream(filename, FileMode.Open))
        {
            try
            {
                SR = File.OpenText(filename);
            }
            catch (Exception ex)
            {
                CCR.ExceptionHandler(ex, "FileQuickRead.FileQuickRead");        
            }
        }
    }  
    catch (Exception exc)
    {
        // If the "using Stream filename" fails
        #if TRACE
            UtilCE.LogInfo.Add2LogFile(string.Format("Catch block in FileQuickRead caught: {0}", exc.Message));
        #endif
    }
}

...The log file never contains the "Catch Block" string, so it's getting past the "using filename" but apparently failing on the call to File.OpenText().

Also, it's failing on the other two methods in the class, namely ReadLn and FileClose:

public string FileReadLn()
{
    try
    {
        aLine = SR.ReadLine();
    }
    catch (Exception ex)
    {
        CCR.ExceptionHandler(ex, "FileQuickRead.FileReadLn");
    }
    return aLine;
}

public void FileClose()
{
    try
    {
        SR.Close();
    }
    catch (Exception ex)
    {
        CCR.ExceptionHandler(ex, "FileQuickRead.FileClose");
    }
}

I get a NullReferenceException on FileQuickRead, FileReadLn, then FileClose, three times in succession.

The only other thing in the class are these global declarations:

private StreamReader SR;
private string aLine;

Callers do so in this way:

fileQuickRead = new FileQuickRead(fn);
// Read the line from the file*
aLine = fileQuickRead.FileReadLn();
. . .
while ((aLine != null) && (aLine != ""))
. . .
    aLine = fileQuickRead.FileReadLn();
    if (aLine == null)
        continue;
. . .
    finally
    {
        fileQuickRead.FileClose();
    }

Is the SR.Close() in the FileClose() method not enough? Do I need to do something to completely flush the file, or...???

• Great - the only comment in the whole project, and it only divulges the achingly obvious.