I can't open the attachment in my ZOHO mail,

I can't open the attachment in my ZOHO mail,

Hello,

I'm a new Zoho CRM user. My CRM is connected with my gmail account and is synchronized.

When I send an email from my gmail account with a PDF attachment to a client it works. 
When I go to this client in ZOHO CRM and open the mail, I can't open the attachment from that mail.
I get the following error in the mail:
=?ISO-8859-1?Q?, followed by the titel of the attachment.

When I open the attachment, I get a blank screen.

I googled the error and from the results of it, I think it is a language error in the attachment but I have no clue how to solve it. Not all the files give this error. I tried to compare the files but couldn't find any differences.

Does anyone have a solution for this problem?

I think the problem is in the file not ZOHO but i thougt i give it a try here.