The layer's symbology is not supported by KML. If not changed, the symbol will be downgraded to a simple symbol. This may adversely affect the rendering of the layer.
Solution
Change the layer's symbology so that it is simple. Polygons should use simple fill symbols.
- Click directly on the symbol in the table of contents. The Symbol Selector dialog box opens.
- Click Edit Symbol in the Current Symbol check box to open the Symbol Property Editor dialog box.
- Choose the Simple Fill Symbol option from the Type list.
- Change the symbol's color, outline color, and outline width as you see fit.
- Click OK in the Symbol Property Editor dialog box.
- Click OK in the Symbol Selector dialog box.
More information
KML feature symbology is a subset of ArcGIS symbology, so some symbols may not translate into KML. The simplest rule to follow when preparing layers for KML is to keep the symbology as simple as possible.
KML polygon features only support simple symbology. KML polygon symbols must be simple color fills, with no patterned fills or hatching. The line symbol for polygon outlines follow the same rules as KML line symbols. Only simple line symbols are supported. Color and line width properties are honored, but additional effects, such as dashes and arrows, are not. Also, multilevel symbols, such as the Railroad symbol, are not supported in KML.
When authoring features to be displayed in KML, symbols should be kept as simple as possible.