forge server won't start up

it keeps stating that the jar file "custom.jar" cannot be found, when it is clearly in the server directory.

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[25.10 11:37:48] [Multicraft] Received start command

[25.10 11:37:48] [Multicraft] Loading server properties

[25.10 11:37:48] [Multicraft] Starting server!

[25.10 11:37:48] [Multicraft] Loaded config for "Special: custom.jar"

[25.10 11:37:48] [Multicraft] JAR file not found, copying from global JAR directory

[25.10 11:37:48] [Multicraft] Failed to copy jarfile from global JAR directory

[25.10 11:37:48] [Multicraft] JAR file not found. Go to "Settings"-"Update Minecraft" to download the JAR file.

[25.10 11:37:48] [Multicraft] Updating eula.txt file

[25.10 11:37:48] [Server] ErrorUnable to access jarfile /custom.jar

[25.10 11:37:48] [Multicraft] Server shut down (starting) 

[25.10 11:37:48] [Multicraft] Restarting crashed server in 2.0 seconds

[25.10 11:37:48] [Multicraft] Looks like a crash, check the server console. Return value: 1