There are some problems with running Drupal on php 5.3. There are five kinds of solutions:

1. Downgrade to php 5.2.6 (not possible in many situations)
2. modify Drupal to change the error level reporting
3. find the latest patches to fix the problems
4. hack Drupal core or contrib yourself to fix the errors (Drupal 6 is already compliant, but not D5)
5. put a timezone in your php.ini to get rid of timezone errors

Drupal 6

2. Modify Drupal's error reporting --already done for Drupal 6

3. Find patches

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