Hello Wayne,
the code you posted do not cause some errors. Probably there is other code which cause this. Could you check in code behind if you are trying to use plus/minus buttons after you diasble it, or maybe in Javascript.

I'm looking forward to hearing from you.

This works:
<ig:WebSlider ID="webslider_PriceSlider" runat="server"
 ContentAlignment="TopOrLeft" EnableTheming="True" Height="60px" Width="275px">

<Thumb ImageUrl="~/Images/slider_handle.gif"

FocusImageUrl="~/Images/slider_handle.gif"

HoverImageUrl="~/Images/slider_handle.gif"
PressedImageUrl="~/Images/slider_handle.gif" />

<AutoPostBackFlags ValueChanged="Async" />
<ClientEvents     ValueChanged="js_webslider_PriceSlider_ValueChanged" />
</ig:WebSlider>

This fails:
<ig:WebSlider ID="webslider_PriceSlider" runat="server"
 ContentAlignment="TopOrLeft" EnableTheming="True" Height="60px" Width="275px" ShowPlusMinusButtons="False">
    <Thumb ImageUrl="~/Images/slider_handle.gif"

FocusImageUrl="~/Images/slider_handle.gif"                  

HoverImageUrl="~/Images/slider_handle.gif"

PressedImageUrl="~/Images/slider_handle.gif" />
<AutoPostBackFlags ValueChanged="Async" />
<ClientEvents     ValueChanged="js_webslider_PriceSlider_ValueChanged" />
</ig:WebSlider>

Adding ShowPlusMinusButtons="False" creates the error condition mentioned in the previous post (on our test server) in our web application that I took-over.  (The original developers are no longer with the company.)  I hope this helps...

Hiding +/- buttons should not cause error. Can you post your markup.

Thank you

Thank you for your reply.

However, after rebuilding the project and updating the website, the web-page fails to load, returning an error 404 (unavailable) in both instances.

I change it back so the +/- button show and the web-page works OK, except the +/- buttons are showing.

Any other suggestions?

Once again, thank you.

Hello Wayne,

setting ShowPlusMinusButtons property to false is enough. Check you markup code to be sure that it is set to false:

<ig:WebSlider ID="WebSlider1" runat="server" ShowPlusMinusButtons="False"></ig:WebSlider>

Another option is to disable it in codebehind:

WebSlider1.ShowPlusMinusButtons = false;

Try to rebuild your project after savind.
Please let me know if this suggestion is working.
Thank you