I have the "chant" spell greyed out in my spellbook...on the descriptions side !
So I click to memorize it ... I rest and still greyed out on both sides...
How to fix that bug ? Other spells work as intended so why this one ...
I already tried to make another save, restart the game...

(Baldur's Gate I Enhanced Edition)

Have you tried casting on yourself? Because on EEs you have to cast chant on yourself. You can't cast it on someone else.

If that's something you had already done, then what is your class and level?

I can't cast it on myself as I just can't get it. I "memorized" the spell, slept but I do not see the spell in the action bar so I can't cast it on me.

My class is warrior/mage/cleric lvl 4/4/5.

Sorry then I am out of thoughts. I created a FMC on BG1:EE and leveled it up and was able to cast chant without any problems. Except that the chant icon looks like it is grayed out on its own. Adding it to the down list, resting, and then pressing F7 revealed the spell for me.

Maybe try the official Beamdog forums. Maybe there is someone there that had this problem before. It would be nice of you if you write back here if you can find a solution.

Ok I will try the beamdog forums and put an answer here if I found something.

Enhanced Edition is the problem. It is a buggy mess.

I do not have so much problems so far except that one :) I have problems with markers on maps but I had those problems even in the previous edition.

In anycase, I have still no solutions for this bug even on beamdog forums :(

All I can say that this is not a persistent problem . Since I own all EEs both on GOG and Steam, I can say that I do not have such problem in any of those versions.

So only thing I can thing of is a corrupted file. To make sure this is not the case, you can do as the following:

Before re-downloading you can check your installer files' MD5 and SHA1 to make sure they are not corrupted.
Re-download the installer files from GOG and check their MD5 or SHA1 again just to make sure.
Install the games into a NEW directory, like "GOG Games/Baldur's Gate EE" (it normally installs as Baldur's Gate Enhanced Edition)
Enable cheat codes if they are not already enabled.
Create a new character and level it up via console (CTRL + Space if I remember correctly. Then just give enough experience)

If that works, you can use your old save and continue from there.

It seems that I am not only one with that problem as someone post something the last month...
https://forums.beamdog.com/discussion/77646/a-greyed-out-spell-in-the-priest-spellbook/p1?new=1

(I had not applied your idea because it will not do the exact same calculations of dice for stats, life / lvl and I do not remember what I have told to each NPC...in what order etc...)