HardKernel after calling IAP

I am trying to read UID value from LPC11xx chip. My code is running ok, until I try to read UID. After that, well after few other things that run on the uC it ends up in HardKernel.
I guess stack overflow or something, but I dont see anything wrong in iap call..

#define IAP_ADDRESS 0x1FFF1FF1

struct iap_commands{
        enum CMD {
                eReadUID = 58
        };
};
unsigned int param_table[5];
unsigned int result_table[5];
typedef void(*iap)(unsigned int [], unsigned int []);
iap iap_entry;


void read_serial_num ()
{
    iap_entry = (iap)IAP_ADDRESS;
    param_table[0] = iap_commands::eReadUID;
    iap_entry (param_table, result_table);
}

It is totally same whether I call this function at the beginning of main or at some other place, it would always end up with HardKernel. Same use case but without call of read_serial_num runs fine.

I am not really near the RAM or ROM limit of uC.

I am using C++. Am I missing some extern "C" somewhere ?