Hi Binoj,

This does be a common issue when directly using string as parameter for transfer xml or html markup string in webservice or WCF service operations.

As in the thread mentioned by Otomii, if you do want to figure out the root cause(the certain character), you can first get a repro(certain string parameter samples that can always cause the issue). Then, use binary search to locate the exact chars that cause the error.

Or alternatively, we can consider some other approaches to avoid this issue. For example, if the HTML you transfer is of xHTML format, you can consider using .NET XElement or XmlElement type to transfer the data. That's the safe way to transfer xml markup data in webservice operations