I have created an order form using Fast Secure Contact Form plugin for my website, in which users may attach a proof of payment, in pdf, doc, txt, gif, jpg, jpeg or png format. The strange thing is that everything works fine, except when a pdf file is attached. When a pdf file is attached (smaller in size than the 1 mb specified) the following message is displayed and no email is sent:
"Internal Server Error. The server encountered an internal error or misconfiguration and was unable to complete your request ...". Sometimes, when I start with my efforts to attach a pdf file, it will work the first time I try, but after that the same "Internal Server Error" message is given time and again. This happens only with pdf attachments, not with any of the other attachment types allowed on the page.
Have tried to disable other plugins but with no success. Can anyone please help?!!