Value Cannot Be Null Parameter Name Value

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VB

I am getting a argument null exception error in one of my subs:

If MD5Text.Text.Contains(labelX12) Then
                       CheckedListBoxControl1.Items.Add(fs.FullName)
                       lblvirus.Text = CheckedListBoxControl1.Items.Count
                   End If

MD5Text.Text = MD5Reader.ReadToEnd and labelx12 is the string that I am comparing to. I have no idea why it is running into a null value when it is always fed information. I have tried to resolve this issue for some time now on my own and have reasearched other sites that tell you to check or uncheck the security settings box for one click security but that does not solve my issue.

Here is the call stack of my particular error:

at System.String.IndexOf(String value, Int32 startIndex, Int32 count, StringComparison comparisonType)
   at System.String.Contains(String value)
   at Final_test.Form1.ScanScanner(String dir) in C:\Users\Admin\Documents\Visual Studio 2010\Projects\Final test\Final test\Form1.vb:line 155
   at Final_test.Form1.starting_scan() in C:\Users\Admin\Documents\Visual Studio 2010\Projects\Final test\Final test\Form1.vb:line 120
   at System.Threading.ExecutionContext.runTryCode(Object userData)
   at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()

Any help would be great thank you!!