Visual Basic 6 recordset value becomes null

I have a vb6 program that pull some information from a SQL 2005 server database.  One of the fields in the database is a remarks field of type varchar(1200).  

When I use a select statement to load the recordset a funny thing seems to be happening.  When I ran my program, which is just comparing values and looking for matches, I received an invalid use of Null error.  I started to debug the program to find the problem and checked to make sure the field was not null.  It was not, but it is exceptionally long (910 characters).

I set a break point to find the values at the time it crashes, and found that when I first broke the program the value for the field is correct.  After about 5 seconds, with no intervention from myself and the program is not running, the value becomes null.

The error is occuring at field number 18 of record number 1525 of my table.  I inserted the following code to try to trace some values:

If x = 1525 and k = 18 Then
    tmpstr = BRS1.Fields(k) 'the field value from the table
    tlen = Len(tmpstr) 'the length of the field
    dummy = 1 'I set a break point here to look at the values
End If

Once I inserted this code, the problem goes away.  Later in my code I use BRS1.Fields(k) and not tmpstr.

Can anyone explain this behavior, I am worried that I may be missing a concept that could cause problems later.
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