[chirp_users] Kenwood TM -281 Chirp not reading from radio.

Tried to down load from radio over passt couple of days.  I get message that stated culd not open port com6: [Error 5] access is denied.  Tried new KPG46 cable and new Tripplite USB to serial adapter and still would not down load.  Then tried it wil the kenwood software and was able to read the radio data.  Is this a known problem?  Any sugestions would be appreciated.   Thnaks   KG7GUK