Symptoms

You may receive such error, for example, from custom application built on SharePoint 2010 which uses K2 blackpearl and SmartForms.

Error message looks like this:
„Surrogate pair (0xD800,0x1783) is invalid. A high surrogate character (0x0800 - 0xDCFF) must always be paired with a low surrogate character (0xDC00 - 0xDFFF). "

This error usually disappears if IIS reset and K2 service restart performed, but may appear again after some time (few hours/days).
 

Diagnoses

There is a known issue with K2 API in version 4.6.6 which may lead to such error and coldfix for it may be obtained from K2 support.
 

Resolution

Please contact K2 support to obtain coldfix for this.