Your db is probably full of 'traps' - minor annoyances for someone trying to help. Like clicking a button to close a form and the whole db closes - poof!
Or your use of special characters in object names, thus your button code fails because of that, and the fact that you don't wrap such (bad) names in brackets. If the brackets get fixed, the code alters the form record source, which doesn't sound anything like what you asked for, which is to set a field value across a set of records.
I've stopped there for the moment but I'll poke around some more.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.