When one of your accounts show you this message, it means that the max amount of simultaneous operations has been reached. What this means specifically is for example if I have set the Max Account Operations to 1 and I have 2 accounts which both have the following module enabled and are both scheduled to run at the same time. Now account A starts scraping users and eventually follow them, however, account B also wants to start scraping users, but because the max operations are set to 1, it will wait till account A has completed the Follow operation before starting.
To increase the max operations, click on the cogwheel top right. You will then see an option called Max Account Operations which will be defaulted to 8. You can modify it to suit your needs. It is advised to set this option to a lower value if your PC won't be able to handle too many accounts. This way you can even have a lot of accounts on lower-end PCs.