the value you entered is not valid for the field

Attachment 21003
vendor is short text, i can save the record normally when i select the value from the combo box because my combox is bounded to vendor field. but also i have created a macro for a button which is next to go for other record. but while viewing other records using next button i can view all the data from the master table.
the issue is if a user wants the value to change from one to another in he combo box then the onchange event triggers and then the value should be updated by old value in the table
similar like this
Attachment 21005
Attachment 21006
also i pulled values from that vendor table to combo box.

The Change should automatically take place without any On Change vba.

Thanks OBP, i have figured it out yesterday and resolved it . As i was validating few fields before the save operation has performed thats why it didnt allow me to save automatically.