Hi Sns,
Based on the command and Dockerfile you provided, it appears there is a typo in the command, which is likely causing the error. The issue is with the --file argument in the acr build command. The correct argument is -f (or --file), not -file.
Here is the corrected command:
acr build acrtasks/ausemartweb:1 --registry acr12345678910 -f Dockerfile
I hope this helps?