Please enter a value with a valid extension.

I have setup VFB, and have to add a resume upload field, which I did. I put in the upload types as your site shows ( pdf | doc | txt ) but when I try to upload a word doc file, it throws that error:
Please enter a value with a valid extension.

I have tried saving the doc as docx, and doc.

http://ww.wp.xz.cn/plugins/visual-form-builder/