This is usually related to a low value in the php directive 'memory_limit'.
Do the following: in global Configuration--> file manager --> base path choose, for example, the 'cli' folder. Save the changes and launch a manual task.
If it ends, it's the memory_limit issue. Increase it (or ask your hosting provider how to do it). A value of 256M is high enough for most sites, but it depends of the number of files.
There is a "trick" to reduce the amount of memory needed; go to Global configuration --> Tuning and set "Scan executable files only" to Yes. After that click on the Initialize Data button at main panel and tell me if it works.
Also check if you have many files into any folder; for example, a customer of mine had more than 20Gb into a folder and this is why the extension were not able to store all data!!
Hi Jose and as always - thanks for the quick response.
I have done both of those things and ran File Integrity and Malware - they ran perfectly. There are no mega files.
I am moving over to a new server in a few days (as I have problems with my current provider) so will see if that makes a difference and let you know.