After releasing a major update to 4.0, Jetpack was inundated with users reporting a fatal error, or white screen while trying to update. Developers quickly spread word to avoid updating to 4.0 after clients began to receive emails that sites were going down across WordPress. A followup, 4.0.2 was pushed out quickly to specifically target the fatal error.
READ MORE // WordPress Pushes 4.2.1 Update
This error marks the third time in less than two months that the Jetpack team has scrambled to push out a followup update on the tail end of a major updating, attempting to correct serious issues. The team worked quickly in each case, getting a fix out quickly to sites with fatal errors.
“We’ve released 4.0.2 that fixes a fatal error that was caused by Jetpack not being able to find a library directory.”
Any issues with Jetpack 4.0 should be corrected by updating to 4.0.2.