Substitution through GGB1 not working

Hi SAP Gurus,

I wrote a substitution through GGB1 under 'Application Area' Financial accouting 'Section' Line item.

Basic requirement is to avoid posting to a particular profit center for the given company code

Prerequisite: If Company code= 5000 and Profit center= CHEM1

Substitute Profit Center= LIQ1

Pasting the exact GGB1 lines:

BSEG-ANFBU = '5000' AND BSEG-PRCTR = 'CHEM1'

Substitute Profit Center= 'LIQ1'

Substitution green light is on,showing no error in syntax.But when I tried to post document in this company code through FB50, system didn't substitute the required profit center (LIQ1).

Any clue why substitution didnt work out? Please help!

thanks

Nellikka