The File you are looking for is inside the @ace folder in the 506th mod pack.
Extract the 506th Modpack v1.7 again. Copy the file "ace_clipboard.dll" from the main @ace folder, paste into your Arma directory @ace folder.
IF that does not work, try a fresh copy of @ace(DELETE old folder. Paste in new one), remembering to apply the hot fix.
*It is known for extract software to corrupt files or not have them extract completely at times.
>If you already have the file and a fresh copy did not work, Antivirus software(norton/bitdefender) firewalls can block .Dll file transfers.
>Make sure you have @ace from the 506th pack.
Hopefully one of the above solves it, feel free to pm!