Adds a new item to the cache store.
id
A System.String that uniquely identifies the cache item to be added.
data
An array of System.Byte representing the item data.
priority
The relative precedence of the cache item expressed by System.Web.Caching.CacheItemPriority. Items with lower cache priority will be removed before items with higher priority.
This method will check whether the item already exists before inserting it. If the item exists this method will throw exception. To force the Cache object to try inserting the cache item call the Insert(string,byte[],cacheitempriority) method.