First you have invalid HTML, you are missing </span> elements at required locations:
<span class="rf-trn-cnt rf-trn-sel"></span>
For your Find Expression, all that you missed is that the values for class are more than just "rf-tr-nd-colps" and "rf-trn-cnt". What you had originally was this:
"class=rf-tr-nd-colps", "|", "class=rf-trn-cnt"
Written that way means the value for class must match exactly
. Since it only contains that, doesn't match exactly the find wasn't finding a true match. We can change it very easily to indicate 'contains" by preceding the text with a ~ character like this:
HtmlFindExpression ProjectLabelInProjectsTree = new HtmlFindExpression("id=projectTree", "|", "class=~rf-tr-nd-colps", "|", "class=~rf-trn-cnt");
Now it will work.
All the best,
the Telerik team