Strange PHP "Allowed memory size exhausted" error

[yaix]

I have a very strange problem with PHP. It complains about "Allowed
memory size of x bytes exhausted", regardless what limit is set in
php.ini.

Even stranger is how it started. I imported some csv-files into a
database. To do that, I set the memory limit in php.ini to some 512MB
and the execution time to some 2 hours.

The script ran out of memory after 90 minutes, and since then, EVERY
script runs out of memory! Even a phpinfo() script, complaining of an
"Allowed memory size of 262144 bytes exhausted" (sometimes even
smaller byte amounts). The php.ini value is still at 512MB, so where
does PHP get those limits from?

Thanks for any hints!