如何从网络Web服务器在网络客户端上创建文件

I have a webserver set up on a business network. I am using php to create a file and I want to write it to a local client shared folder also on the network. When I ping from the client I get a response from the webserver. When I ping from the webserver I get a response from the client. Here's my code. I am getting a permissions error. Any ideas what could cause that? Is the path correct? How do I formulate the path?I have a webserver set up on a business network