Every time I delete a spammer (delete their activity, blank their profile and suspend their account) it then displays an 'Error writing to database' error.

It's only started happening recently; I don't know when it first started. The delete spammer script still appears to work.

In order to check the logs, I'm noting a time when I deleted a spammer:
Tue 8 October 2013, 9:28 AM CET (07:28 UTC)