This field shows the general posting type that will be used when you post the entry on this journal line.
The program automatically retrieves the general posting type from the General Posting Type field on the G/L account card if you insert a G/L account in the account no. field.
The program uses the general posting type, together with the VAT Bus.Posting group and VAT prod posting group fields, to find the account to which VAT is posted.
To see the general posting types that are available, click the AssistButton in the field:
Use this option if the transaction on this journal line does not involve VAT.
Purchase
Use this option if the entry on this journal line contains a purchase transaction. The program uses this information to calculate the correct purchase VAT and post it to the account for purchase VAT.
Sale
Use this option if the entry on this journal line contains a sales transaction. The program uses this information to calculate the correct sales VAT and post it to the account for sales VAT.
I made CST payable Gen. Posting type as sales. Till now no user reported the error regarding that transaction. The question remains why it showing error for the GL account which has Gen. Posting type( refer to my first post, I have kept message for displaying gl account is it a bug).