Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
@KGahbiche I replaced Lists parameter to "<Lists><List ID=\"" + lib.Id.ToString("D").ToUpper() + "\"/></Lists>". Result Lists string is: "<Lists><List ID="9027A315-0B24-4278-BC54-8C6D6BBC8C85"/></Lists>". I've checked list, it has same id and there is one task in this list. But result is still empty.