How to change the text of a label?

Try this:

$('[id$=lblVessel]').text("NewText");

The id$= will match the elements that end with that text, which is how ASP.NET auto-generates IDs. You can make it safer using span[id=$=lblVessel] but usually this isn't necessary.

I was having the same problem because i was using

$("#LabelID").val("some value");

I learned that you can either use the provisional jquery method to clear it first then append:

$("#LabelID").empty();
$("#LabelID").append("some Text");

Or conventionaly, you could use:

$("#LabelID").text("some value");

OR

$("#LabelID").html("some value");

ASP.Net automatically generates unique client IDs for server-side controls.

Change it to

 $('#<%= lblVessel.ClientID %>')

In ASP.Net 4.0, you could also set the ClientIDMode property to Static instead.