For some reason I now have this message for several tasks.

"09/06/2020 09:51:53 | climateprediction.net | Task wah2_anz50_31cz_209412_32_872_012026751_0 postponed for 600 seconds: Waiting to acquire slot directory lock. Another instance may be running."

Can someone tell me how to get the tasks running again please?

Thanks.

Try getting task manager up and see what BOINC processes are running. It may be that somehow there are two instances of the client running.

https://boinc.mundayweb.com/wiki/index.php?title=What_do_Suspended,_Waiting_and_Postponed_mean%3F

In their FAQ they state

Postponed: waiting to acquire lock

This message means that a previous task is still occupying the lock file in the slot directory. BOINC cannot continue with this task until that slot directory has been vacated. Try to reboot, that usually stirs things loose. Used in BOINC 7.

Thanks for your help Dave.
The Task Manager showed only one BOINC running, so that was not the problem.

However, the REBOOT cleared my computer's confusion (and mine!).
Tasks now running again.

Thanks for your help Dave.
The Task Manager showed only one BOINC running, so that was not the problem.

However, the REBOOT cleared my computer's confusion (and mine!).
Tasks now running again.

I think the root of the problem is a corrupted lockfile. The slot directories are deleted on shutdown and recreated when needed. I haven't used Windows for too long to be sure (totally defenestrated in 1999) but you can probably also sort it by going to the slot directory and deleting the lock file there. Not sure if it is a hidden directory or not. It isn't hidden on Linux but as I say my Windows knowledge is very out of date!

The BOINC slot directory is in the Program Data folder which by default in W10 is hidden.