A programmer reports this problem when using PHP: “It didn’t take me long to find out that if you use flat files to read and write, you should change their settings. They’re set to read, not write, so...

A programmer reports this problem when using PHP: “It didn’t take me long to find out that if you use flat files to read and write, you should change their settings. They’re set to read, not write, so just click Properties to change their settings. To save time, if I saw an error I didn’t understand, I Googled it.” What kind of error is it? What rules were applied, and which should have been applied earlier?