I'm not sure what the criteria for whether the button should show would be. It appears that it's just if the Windows username is in the username_assignment_t table.
If so, then I think all you need is to check whether any records with that name exist:
If DCount("*", "username_assignment_t"...
As far as having checkboxes for records that the user can select records to be copied is concerned:
You're hitting on a bit of a limitation of Access - I'm expecting you mean a continuous form or datasheet with checkboxes on each record. The checkboxes can't be bound to a calculated field...
Previously on The Story:
"Yippeeeeee"
"Ouch"
"What the **** are you trying to do?"
"For **** sake! How could someone eat a pineapple made of poo?"
"What the hell am I!? gay or straight? Dressed like an Access Forum Member."
"Eureka! I found a wooden spoon"
"..........oops!"
"Will i dance!?"...
Both are great suggestions and I wish I'd thought of them.
I've been typing it out by hand. :D
Nah, not really, I've been taking screenprints, printing to pdf and then putting that through FreeOCR. I'm no fule.
Previously on The Story:
"Yippeeeeee"
"Ouch"
"What the **** are you trying to do?"
"For **** sake! How could someone eat a pineapple made of poo?"
"What the hell am I!? gay or straight? Dressed like an Access Forum Member."
...they realised that the Tv Licence had been sold to the highest...