can you check by installing keil 4 software from
Keil Embedded Development Tools for ARM, Cortex-M, Cortex-R4, 8051, C166, and 251 processor families.
I think it is a bug in the software.
or
250 KHz is the default JTAG speed Red Suite uses for ARM7. In practice, allowable rates are dependent on the core clock. Adaptive clocking is available for those chips which support RTCK. Refer to your processor User's Manual for this information. Adaptive clocking may not be available if your application has reprogrammed the RTCK pin as GPIO, or the reset pin state is not RTCK. NXP ARM7 variants which support RTCK are:
•LPC22xx •LPC23xx •LPC24xx •LPC21xx If adaptive clocking is not available, the general rule for Maximum JTAG speed is one sixth (1/6) the core clock frequency. The frequencies used by the ISP firmware can vary across families, so refer to the documentation. As an example, a safe JTAG speed for the LPC2148 (no RTCK) when booted into the ISP is below 2000KHz. Red Suite offers a "Configuration Option" to preset the NXP ARM7 core clock frequency in the project Debug Configuration.
The name of this setting is "Crystal (XTAL) frequency and PLL value" and the input format for this information is XTAL,FREQ.
As an example, if your ARM7 board has a 12 MHz crystal, and the desired core clock frequency is 50 MHz you'd enter:
12000, 50000. An internal Red Suite algorithm will attempt to setup the core clock as close as possible to the value requested.
Note that if an attempt to connect at a particular JTAG speed fails, follow-on attempts at lower speeds may fail. Should this happen, cycle the power to the ARM7 and Red Probe in the sequence documented above.