Using GL fast entry to post asset transaction

Hi All,

I'm using SAP 4.6C, and I want to make some asset purchasing through FI postings. using tcode F-02.

I want to use GL fast entry feature to do this.

Posting key = 70

Account = asset number

trans typ = 100

But I'm facing error message "Enter a posting key for G/L accounts" Message no. F5 219.

I don't understand where is my mistake.

Regards,

Melissa