Problem about mod signing...

Hello,

I tried to sign a mod with ForgeGradle :

apply plugin: 'signing'

// ...

signing {
    sign tasks.jar
}

(I supplied the key ID, the password and the PGP keys to the gradle.properties file)

I supplied the fingerprint to the @Mod.

But when I run :

gradlew build

(It runs without errors)

And then I run Minecraft with the builded mod, the FMLFingerprintViolationEvent is fired...

How can I resolve this ?

PS : Sorry for the bad english, I usually speak french...