Error reading from a dat file with C#

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.NET3.5

C#

.NET

hi,
i have created a very large dat file which contains sine wave values in it, but when i try to read from this file in order to plot while checking the eof condition with:
while (br.PeekChar()!=-1)
{
//read
}
I get the error:
"The output char buffer is too small to contain the decoded characters, encoding 'Unicode (UTF-8)' fallback 'System.Text.DecoderReplacementFallback'".

Please tell me how to resolve this?

P.S any way to use blob object here?