[HELP] Unusual script timeout error

Hi all,

I'm having problem with the classic error:
"<b>Fatal error</b>: Maximum execution time of 30 seconds exceeded in
<b>Unknown</b> on line <b>0</b><br>"

I'm doing a database (mySQL) intensive operation of fetching,
processing and updating.. around +/- 30.000 records, it usually takes
about 15-30 minutes daily. It works fine,.. but on certain (random)
occasion, after the script finishes all the operations, it printed the
above error,...

I don't know where i've done wrong, I've make sure that:
1. set_time_limit(0) on the .php script
2. maximum_execution_time = 0 (in php.ini)
3. safe_mode = Off (in php.ini)
What confuses me, is why does it print "Unknown on line 0" instead of
the filename?

Here's my spec:
PHP version: 4.2.1
Apache : 1.3.26

Any suggestion or help or anything :) .. would be appreciated. Thanks

Cordially yours,
Hendry Johan