Inscrutable Exception From StreamReader

[bullshark]

The code ran for 133 hours without failing. This would be the 267th
iteration of the (same) object and the code below is used 5 times
per iteration giving 1335 cycles. It was halfway through current
iteration at fail.
The raised exception (see below) does not seem to be documented
or under my control. It appears that methods internal to the
StreamReader class have failed.

Any idea if this is a bug or known problem?

string ReadResp(Stream stream,Encoding encoding,bool print, bool stop){
StreamReader reader=new StreamReader(stream,encoding);
char[] read=new char[256];
int count;
StringBuilder str=new StringBuilder("");
count=reader.Read(read,0,256); //Exception thrown here
while(count > 0){
str.Append(read);
count=reader.Read(read,0,256); // Or here...
}
response=str.ToString();
if( print )
Console.WriteLine(response);
if(stop){
Console.WriteLine("Press Enter to continue.");
Console.ReadLine();
}
return response;
}

Main Exception raised!
Source :mscorlib
Message :Non-negative number required.
Parameter name: byteCount
at System.Text.ASCIIEncoding.GetChars(Byte[] bytes, Int32 byteIndex, Int32 byteCount, Char[] chars, Int32 charIndex)
at System.Text.DefaultDecoder.GetChars(Byte[] bytes, Int32 byteIndex, Int32 byteCount, Char[] chars, Int32 charIndex)
at System.IO.StreamReader.ReadBuffer(Char[] userBuffer, Int32 userOffset, Int32 desiredChars, Boolean& readToUserBuffer)
at System.IO.StreamReader.Read(Char[] buffer, Int32 index, Int32 count)
at WebCleaner.WebCleaner.ReadResp(Stream stream, Encoding encoding, Boolean print, Boolean stop)
regards,

bullshark