Hi thoughtstorm,
Thanks for your feedback and really sorry for the late reply.
First of all, please check if you are under Remote Connection Mode. You can check the connection mode in the bottom right corner:
1. Do you use VPN? If yes, you may disable it and try again.
2. Would you please try to ping the IP address displayed on AirDroid app on your device?
If you are using Windows, you may click the Start button and enter "cmd" into the Search field. If the IP address displayed on AirDroid app is 192.168.xx.xxx, then you can type ping 192.168.xx.xxx -t and press enter to see your ping output. And you may refer to the guide here for other OS:
http://www.wikihow.com/Ping-an-IP-Address
If the ping output isn't ideal, then the connection would be Remote Connection Mode. There are many factors that cause this and sorry that we cannot help you in this. We advice you to ask for help form network admin.
As to the "Attach a file", you have to click "Attach a file", select the file you want to attach (let's say a picture) and hover your mouse on the picture. Click "Insert Image" under the picture.