Random 500 error

[eluser]Unknown[/eluser]
Recently a program I have written is throwing a 500 error.
At random times.

I tried exiting the code in different places to see "where" it was breaking.
But it seems to be breaking in random places.

Also the 500 error returns no error. And the Apache logs are empty.

The code WAS working. And hasn't changed, but the error is happening progressively more often.

'Any ideas..'?

[eluser]Unknown[/eluser]
Think I figured it out.
Was sending POST data via AJAX. But large amount. So Server was making it GET.