The PSSS service uses PI SDK to communicate with the PI Server. PI SDK is implemented according to the Microsoft COM standard that represents strings as Unicode characters using UTF16 encoding. Moreover, based on COM Tech, like C++, cannot convert UTF8 to UTF16 automatically. This might needs your own way to complete the converting. After this, you could use the UTF16 string as the parameter for the UpdateValue method.
thank you for your answer.
I did the UTF8 string conversion in UTF16 and use it as the parameter of the UpdateValue and it works fine.
Thank you very much.