Differences between LoadRunner logs and apache logs

Hi.

I got a problem of differeces between LR logs and apache logs.

My load test of 15 VU was 5 successful and 15 failed.

LR outputs 14 "HTTP/1.0 502 Bad Gateway".

But apache outputs 11 "HTTP/1.1 200"  in the same pages.

Anyone knows why differences like this are caused?

By the way, my load test probably failed becase of high cpu usage.

Thanks in advance.