That was definitely the problem. The enumerator is really just a 'sizer' for an array so setting it to false does not make sense. The enum provides you offsets based on items preceding it, making it easy and fast to work with constants/variable-names to access items in an array. Setting to false for something would need to be done on the g_PlayerData[] array that was sized by playerTable.
The enum items in playerTable hold the below values. If the compiler allowed this, doing "isOnline = false" would change its value from 125 to 0 which essentially would over-write data where 'nick' is stored.