Extended Slider Error coming up in FF but not in IE

Hi All, 

I am getting a couple of errors that are coming in FF and Chrome but not in IE. Errors are the following:

Sys.ArgumentException: Sys.ArgumentException: Please set valid values for the height and width attributes in the slider's CSS classes Parameter name: element size

And second one is : Sys.ArgumentNullException: Sys.ArgumentNullException: Value cannot be null. Parameter name: handler

Here's my code: 

AjaxControlToolkit.SliderExtender seHBP = new AjaxControlToolkit.SliderExtender();
                                    seHBP.ID = "seHBP" + r.RowIndex + hbp.companyValueId + hbp.competencyId;
                                    seHBP.TargetControlID = txtHBPCompetency.UniqueID;
                                    seHBP.BoundControlID = txtHBPBoundCompetency.UniqueID;
                                    seHBP.BehaviorID = txtHBPCompetency.UniqueID;
                                    seHBP.Minimum = 1;
                                    seHBP.Maximum = 5;

Any help will be much appriciated. 

Thanks,

Attiqe