Each time I vacuum, I get an error message that reads: Unable to execute query: Reason: Fatal Error (ERROR: could not read block 7933 of relation base/16395/58203: Input/output error)

How can I fix this?

Please run Database > Housekeeping with just the ReIndex option enabled.

If that doesn't fix it then the second reason for this error is a result of faulty hardware. You can set PostgreSQL to ignore these errors by clicking Start --> Programs --> PostgreSQL --> Configuration Files --> Edit postgresql.conf. In the configuration file that appears, go to the bottom of the file and add the text “zero_damaged_pages = on” on a new line and then save and close the file. Click Start --> Programs --> PostgreSQL --> Reload Configuration and PostgreSQL will ignore the damaged data. If you continue to have problems with that hard drive, you should consider replacing it.

I have reindexed, and that did not fix it. How do I find the configuration files on Mac?

The file is located in /Library/PostgreSQL/8.4/data/ on a Mac.

When I go to that folder, my computer won't let me open it. What should I do?

On the bottom right hand corner of the "data" folder there is a little red circle with a minus sign in it.

Anyone know?

You'll need to give your user Read & Write access to the directory as explained here.

Kraada, everything worked out. Thank you for your help!

Glad to hear it!