Reporting logs and poison message

I have a report that uses multiple layers with multiple levels of joins (Detail Report). Things were going well, but for no apparent reason, now everythings seems to crumble apart. I can't run the report anymore with even a single Detail report. I'm getting almost always the Poison Message error.
I would like to look at the server logs for reporting, but I can't find them. I need to know exactly what is causing the report to fail if I'm going to fix it.
Anyone knows where I can find them?