Where is your error handling? The GetListEntry-call should give you exact information if it fails.
And why have you complicated bilding your qualifier string, make sure not to concatenate more strings than needed? And use the field id instead to be sure of what you get:
strSQL = "'536870913' = \"" + changeInput.Text + "\"";
We might need more hel, as I am not much of a C# programmer...
Best Regards - Misi, RRR AB, http://rrr.se