This article lists known issues in the RadMultiColumnComboBox control.
R2 2019 release introduces the Design-time for the RadMultiColumnComboBox control. The issue is present only in earlier versions.
RadMultiColumnComboBox does not support design-time at the moment.
When you open the Design-time surface of Visual Studio, RadMultiColumnComboBox instances will not render and will throw the
Failed to create designer error.
R2 2019 release introduces multiple skins for the RadMultiColumnComboBox control. The issue is present only in earlier versions.
RadMultiColumnComboBox supports only the Default skin.
Setting a different skin name will result in a runtime error like
Telerik.Web.UI.RadMultiColumnComboBox with ID='RadMultiColumnComboBox1' was unable to find an embedded skin with the name 'WebBlue'. Please, make sure that the skin name is spelled correctly and that you have added a reference to the Telerik.Web.UI.Skins.dll assembly in your project. If you want to use a custom skin, set EnableEmbeddedSkins=false..