No item category assigned to account

Hi,

Account 300400 has been already assigned to the item category and we have already made posting to this account without any errors before.

While posting through FB50, user is getting the error message:

"No item category is assigned to account 300400"

Message no. GLT2076

Diagnosis

The online document splitting is active in your system. Here, each document is assigned to a accounting transaction variant and each document row to an item category.
You determine for each business transaction variant which item categories can or must be posted here.

The following error occurred for the document you entered:

No item category could be determined for account 300400 in chart of accounts

System Response

The document cannot be posted.

Procedure

Assign an item category to the account specified. You do this in Customizing for Document Splitting under Classify G/L Accounts for Document Splitting.

What could be the problem?

Regards,