File Upload validation message

What are the EXACT steps you do to make this happen?

1. I am trying to upload an invalid file, such as a .sql file.
2. I get the error message mentioned above.
3. After that, I try uploading a valid .pdf file, but the above validation message still appears.
4. When I upload a valid file, the validation message should not appear, but it still shows up when I try to upload a valid one.

OK. This "after that", what exactly is that?

The reason I ask is that when you try to set the variable value to NULL from external, then the internal state of that field does not get updated correctly. That is a known issue. If you use the control inside the file upload field, this should work.

That glitch only happens in the interface designer, not when the interface is used in an assigned task.

Could you please share the code snippet of how you are evaluating the validation and also let us know if you are uploading multiple files to check at once or single file at a time and evaluating, for our better understanding.

Could you please share the code snippet of how you are evaluating the validation and also let us know if you are uploading multiple files to check at once or single file at a time and evaluating, for our better understanding.

I believe this relates to a long-standing known issue with the system-level validation message that fires when such a document is uploaded.  For instance in my system we disallow the ".heic" extension to prevent space wastage, and (in interface designer) the validation message fails to clear even if I replace it with a completely valid file.  As OP noted though, this doesn't appear to be happening in actual tasks, just in the designer.

a!localVariables(
  
  local!doc,
  
  a!fileUploadField(
    value: local!doc,
    saveInto: local!doc,
    maxSelections: 1
  )
)