This is a standard WordPress error message. Usually this is caused by another plugin blocking the BPS Pro upgrade, but can be caused by other things like corrupt Browser cache or some function in your Theme.
How are you trying to upgrade BPS Pro? Using the WP Dashboard upgrade/update link? Clear your Browser cache and plugin cache if you have a caching plugin and try the upgrade again. Deactivate all plugins except for BPS Pro and try and upgrade again.
Well what can happen randomly and may not really be an issue or problem with a particular plugin and is some kind of WordPress DB transient cache issue. Something like a transient cache is out of whack or corrupted. Deactivating all plugins clears the WordPress DB transient cache or whatever transient cache is out of whack. Without actually taking this apart and figuring out the exact technical aspects of this issue are, I am just laying this out in simple laymans terms. 😉