You really should consider using SqlParameters. It's easier to write, easier to read/debug and more secure. Adding variables as a part of a sql-query will make it vulnerable for sql-injections.
But to debug this, the first thing I would do is to see the result of
strUpdateQuery
variable before it is executed. You will see what's wrong if you see what you are trying to execute.
And why are you doing ordering in an update query?
"ORDER BY tblRoutingMain.ROUTING ASC"