Base material group contains characters that are not permitted

What causes this issue?

You have used special characters. These are not allowed.
You cannot use the characters "!", "$", "%", "&", "=", ".", ",", ";",
"?", "*", "#" and the blank character.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

INCLUDE ISR_CHECK

Error message extract from SAP system. Copyright SAP SE.