Attachment is not working if it is greater 2KB

Dear Support,

When I try to attach file [Notes/Email Activities] it is showing page cannot be displayed error. It is working fine if the file size is less than 2KB. I have checked the system settings and it is set to maximum. Also I have checked some other users and there it is working fine. Anybody can tell what would be reason for this?

Really confused with this

Please help

Thanks