Scheduled membership reminders have stopped working

Scheduled reminders have stopped working since 1st June 2016 and appear to have done so since updating CiviCRM to v4.7.7 and v4.7.8. The following error message is in the scheduled jobs log: "Summary Finished execution of Send Scheduled Reminders with result: Failure, Error message: Cannot build query. Variable "@memberTypeValues" is unknown. Details Parameters parsed (and passed to API method): a:1:

Full message: Finished execution of Send Scheduled Reminders with result: Failure, Error message: Cannot build query. Variable "@memberTypeValues" is unknown"

Other points to note:

• Wordpress version 4.5.2 (since updated to v 4.5.3)
• Other CRON is working OK
• No extensions are installed
• Scheduled mailings are going out OK
• No changes have been made to member types

I have asked for advice on StackExchange but have not received an answer, although one helpful person did ask me to look for any errors in /files/civicrm/ConfigAndLog and for any PHP error log. There were no errors found. I've contacted my host to see if there are any php errors in the log. Although there was initially a security issue whereby my IP address was blocked, they have cured that and said "now the security rule triggered is fixed, there seems to be a remaining issue and it looks to be to do with how CiviCRM is coded".

Scheduled reminders are still not going out as part of the CRON job, and the above error message is still appearing when the job is fired manually.

Can anyone tell me please whether there are any known bugs?
Many thanks