illegal implicit conversion from 'const unsigned char *'

_LIT8(KDesKey,"12345678");
TBuf8<8> deskey;
deskey.Copy(KDesKey);

unsigned char* pdata = deskey.Ptr();

最后一行始终提示：
1337483950207 illegal implicit conversion from 'const unsigned char *'
错误，

unsigned char* pdata = (unsigned char*)deskey.Ptr();//不让转就强转反正类型是一样的