What is the meaning of "deassert" in this context?

Solution 1:

My best translation would be 'Stopped signaling'.

Say I have an alarm button. I can push this button to send a signal. Then I release the button to stop sending that signal. Replace 'push' with 'assert' and 'release' with 'de-assert' and you get the meaning.

Solution 2:

I'm not sure where this term started gaining usage in regards to error conditions, but I've seen it with several vendors.

Basically, an error condition is present if it is "asserted". Then if at some point the error condition ceases to exist, a message is logged that said condition is deasserted.

Solution 3:

Further to ErikA's answer...

This terminology carries "up" from digital logic. When you say that a digital signal is "asserted" it's the same as saying it represents a binary value of 1. De-asserted is the same as binary 0.

In your case, the message means that signal IERR was set to 0, i.e. turned off.