jlink program error

When I want to connect the jlink use j-flash.exe.it report the follow message.My 

Connecting ...
- Connecting via USB to J-Link device 0
- Target interface speed: 4000 kHz (Fixed)
- VTarget = 3.345V
- Initializing CPU core (Init sequence) ...
- ERROR: Could not perform target reset
- ERROR: Failed to connect.
Could not perform custom init sequence.

and when I use the bat file to program it report the follow:

ERROR: JLinkARM DLL reported an error. Try again. If error condition
ERROR: persists, run the same command again with argument --log, contact Nordic
ERROR: Semiconductor and provide the generated log.log file to them.

So how to deal with it?