The message received from the server could not be parsed.

I have an issue where if i write the below code:
Dim Context As HttpContext = HttpContext.Current
For Each dc As DataColumn In MyDs.Tables(0).Columns    Context.Response.Write(dc.ColumnName) Next
I get the error:
Microsoft JScript runtime error: Sys.WebForms.PageRequestManagerParserErrorException: The message received from the server could not be parsed.
Removing the
Context.Response.Write(dc.ColumnName)
line, resolves the problem but not sure how to get over this issue?
Thanks
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