How to Apply theme to a sharepoint site using WCF service?

I am trying to apply a theme to a sharepoint site.
my method is as follows :

public void ApplyCustomeTheme(string url, string themeName)
{
using (SPSite oSite = new SPSite(url))
{
using (SPWeb oWeb = oSite.OpenWeb())
{
System.Collections.ObjectModel.ReadOnlyCollection oThemes =
ThmxTheme.GetManagedThemes(oSite);
// list out all themes of this particular site
foreach (ThmxTheme oTheme in oThemes)
{
// Apply my custom theme to the current website
if (oTheme.Name == themeName)
{
ThmxTheme.SetThemeUrlForWeb(oWeb, oTheme.ServerRelativeUrl);
}
}
}
}
}

but when i try to run the WCF client i get the following error:
Could not load file or assembly 'Microsoft.SharePoint.Search' or one of its dependencies. An attempt was made to load a program with an incorrect format.
I have included the 'Microsoft.SharePoint.Search' dll in the References.

Can some one please explain me what is causing this ?. Is it because of serialization ?
Can i get a solution on this ?

Shoeb Sayyed