river merge step in basin processing using ArcGIS via the Hec-GeoHMS extension

[ssarch 0]

Hello! I use the Hec-GeoHMS 10.1 extension in ArcGIS 10.1. After merging 65 subbasins into one basin, I'm trying to river merge all individual streams unsuccessfully. The message from the above action is: disconnected rivers or rivers meeting at confluence can not be merged. I notice that all individual streams are meeting at a confluence. I would like to ask if I'm doing something wrong or if there is an alternative methodology in order to merge all rivers in one.