MyDatabase is not a "networkable" application - it is designed for use on a single system with only one user allowed to access and modify a database file saved on the PC's local hard drive.
You cannot open a MyDatabase file from a server or other networked location without risking file corruption. You also cannot have multiple users open and access a file at the same time.
If you need this functionality, you will want to obtain our Database Professional program. This advanced version allows for multi-user access as well as networkability for opening and saving databases to and from servers or other PCs on your network. If you have information saved in a MyDatabase file and you wish to migrate it to Database Professional, you can do so by exporting your data and importing it using the Import and Export commands of these programs in their File menus.