用Keil时老报这种错，请各们帮看看

编译时老出这种错，Device换过一些大容量的CPU也没用。

Build target 'Target 1'
compiling xxx.c...
linking...
BL51 BANKED LINKER/LOCATER V6.05 - SN: Eval Version
COPYRIGHT KEIL ELEKTRONIK GmbH 1987 - 2007
COMMON {"xxx.obj"}
TO "xxx" BankArea(0x0000,0xFFFF)
RAMSIZE(256)
*** FATAL ERROR L210: I/O ERROR ON INPUT FILE:
EXCEPTION 0021H: PATH OR FILE NOT FOUND
FILE: C:\KEIL\C51\LIB\L51_BANK.OBJ
Target not created