IAR下载时出现这个  J-Link Failed to get CPU status after 4 retries Retry   什么情况啊 ？  怎么处理呢？  谢谢!!
出现如下Log请帮助分析。
Thu Dec 17, 2015 16:54:55: Device "STM32F407ZG" selected (1024 KB flash, 128 KB RAM).
Thu Dec 17, 2015 16:54:55: DLL version: V4.70a, compiled May 14 2013 09:08:53
Thu Dec 17, 2015 16:54:55: Firmware: J-Link ARM V8 compiled Nov 25 2013 19:20:08
Thu Dec 17, 2015 16:54:55: Selecting SWD as current target interface.
Thu Dec 17, 2015 16:54:55: JTAG speed is initially set to: 32 kHz
Thu Dec 17, 2015 16:54:55: STM32F2xxx/STM32F4xxx: Can not attach to CPU. Trying connect under reset.
Thu Dec 17, 2015 16:54:55: Hardware reset with strategy 0 was performed
Thu Dec 17, 2015 16:54:55: Initial reset was performed
Thu Dec 17, 2015 16:54:56: STM32F2xxx/STM32F4xxx: Can not attach to CPU. Trying connect under reset.
Thu Dec 17, 2015 16:54:56: STM32F2xxx/STM32F4xxx: Can not attach to CPU. Trying connect under reset.
Thu Dec 17, 2015 16:54:57: STM32F2xxx/STM32F4xxx: Can not attach to CPU. Trying connect under reset.
Thu Dec 17, 2015 16:54:57: STM32F2xxx/STM32F4xxx: Can not attach to CPU. Trying connect under reset.
Thu Dec 17, 2015 16:54:58: STM32F2xxx/STM32F4xxx: Can not attach to CPU. Trying connect under reset.
Thu Dec 17, 2015 16:54:58: STM32F2xxx/STM32F4xxx: Can not attach to CPU. Trying connect under reset.
Thu Dec 17, 2015 16:54:59: STM32F2xxx/STM32F4xxx: Can not attach to CPU. Trying connect under reset.
Thu Dec 17, 2015 16:54:59: STM32F2xxx/STM32F4xxx: Can not attach to CPU. Trying connect under reset.
Thu Dec 17, 2015 16:55:00: STM32F2xxx/STM32F4xxx: Can not attach to CPU. Trying connect under reset.
Thu Dec 17, 2015 16:55:49: Fatal error:    Session aborted!
Thu Dec 17, 2015 16:55:49: Failed to load flash loader: D:Program FilesIAR SystemsEmbedded Workbench 6.5armconfigflashloaderSTFlashSTM32F4xxx.flash
Thu Dec 17, 2015 16:56:00: Fatal error: Unknown exception in driver 4   Session aborted!