Unfortunately, it’s unlikely that file permissions are related to any change we made in the 4.0 release. I don’t know how they might have been set incorrectly, though if you’ve used any plugin installer or tool to add a plugin or update your site in the past, that might have been the cause.
You or someone who manages your server needs to go into the bp-core/classes/ folder, view the file permissions, and change those of the phpmailer file to match the other files which are (presumably) correct.
OK thanks we will try that and come back if there is anything that might be of interest to others.
I have the same problem, although I am trying to update to 4.1.0 and the filename is not called out in the error message. I checked and confirmed that class-bp-phpmailer.php’s protection is 0000, so I am guessing this is the problem file. But I can’t seem to change it back to 0644 in my file manager, it just seems to reset itself to 0000. Do you think it is possible this class file is locked by a plugin?
It turned out I needed to enlist the help of hosting support to change the protection on that file. No idea how its protection got changed. But once it was reset to 0644 the 4.1.0 update completed with no problems.