floating point in cortex m0, always reset.

hi,I write an algorithm running in cortex M0. It has some floating point multiplication.But the program always resets when encounter a floating point multiplication.And the code showed below:

    for (k = 0; k < 4; k++) {
                        tmpx =   dbuffer[0] * a[k + 1];
                        dbuffer[k + 1] = dbuffer[k + 1] - tmpx;
    }

dbuffer[] and a[] are float array. tmpx is a float variable. When I debug the program, the M0 resets at line "tmpx = dbuffer[0] * a[k + 1];" .And the value of dbuffer[0] is 1429983,a[k+1] is 0.00974910986.
I have tested this multiplication in a new project.And the code goes well and result is right.The test code is like below:

            float a = 1429983;
            float b = 0.00974910986;
            float c;
            c = a* b;

So, I know M0 use softVFP. I have seen asm code such as __aeabi_fmul corresponding to my code.
Could anybody tell me what's wrong with my code?
Thank you very much.