Why file field button disappeared while uploading file? I have installed fresh drupal-7 and create file upload field with manage field with 8M Maximum upload size. when i upload a file 25MB then it is showing error message and file field missing.
Before upload:

After Upload:


After long search i got some links
&quot;exceeded the maximum file size&quot; error even when uploading small files
File upload error &quot;Files must be less than x MB&quot; despite file being smaller than x
By these link my problem sorted out but my question. why the file upload field button  disappeared?.
My php.ini settings are

post_max_size = 24M
upload_max_filesize = 512M
Don't set upload_max_filesize larger than post_max_size if you are not using any library that takes care for such cases. Plupload integration with FileField Sources Plupload can get it managed for you.

Currently you are confusing your Drupal by allowing file upload larger than allowed data size. Given that data posted is file size + metadata size, both always equal to or greater than 0, it makes no sense and Drupal may fail.

Specifically, button disappeared because Form or Field API crashed, and it crashed because you mismatched sizes without providing appropriate handler.