Notice: Undefined index: id in C:\inetpub\wwwroot\crm.hcpro.pt\imgs\clientes\zip_folders.php on line 14

Error: Unable to send file fotosclientes.zip. Output buffer contains the following text (typically warnings or errors):
<br /> <b>Notice</b>: Undefined index: id in <b>C:\inetpub\wwwroot\crm.hcpro.pt\imgs\clientes\zip_folders.php</b> on line <b>14</b><br />