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I have checked your form and found that you have entered jpg extension for two times.You can remove one to slove the problem.
Please see the image below.
You can also validate your image by enabled it.
Please get back to us if you need further assistance.
That is how i managed a problem when i put it one more time at the end.
I tested your form and it is uploading jpg with no problem:
If you need further support please let us know.