If I use this method:https://www.drivehq.com/mapdrive/WebDAVdrivemapping.aspx

...then I get this error:

System error 1219 has occurred.
 Multiple connections to a server or shared resource by the same user,
 using more than one user name, are not allowed. Disconnect all
 previous connections to the server or shared resource and try
 again..

Why o why?? I'm not logged on elsewhere to drivehq. Could it be a problem if other people on the same IP-address are logged on to drivehq or even just have the site open in the browser?

It is well known that regular WebDAV is not reliable. The Windows WebDAV client (i.e. Windows Explorer) has a lot of bugs in authenticating user accounts. For example:

(1) If you have mapped a drive using USERNAME1, then you cannot map another drive using USERNAME2.

(2) Even if you have disconnected the first drive, you still cannot map a new drive using USERNAME2 because Windows somehow caches the first account information.

(3) If you try to open an MS Office file in a WebDAV drive, you will be asked to provide your username and password again.

(4) A drive may become disconnected after you reboot your computer, and it may not automatically reconnect even if you set it to automatically reconnect.

(5) On Windows XP, you must follow the instructions step by step exactly.  If you try to map a drive without providing the correct username and password for the first time, then all subsequent attempts will fail until you reboot your computer!

Luckily, DriveHQ's Enterprise WebDAV Solution has solved all these problems. It is extremely easy, and it does not require any client software, and it works on almost all platforms, such as Windows, MAC, Linux, iPhone, iPad, Android, Windows Phone and Windows 8 RT, etc.

It is better than any other WebDAV solutions available in the market place. To use our enterprise WebDAV service, you just need to order a paid subscription - the price starts at only $1.99/month. For more information about our Enterprise WebDAV service, please visit:

http://www.drivehq.com/help/doc/EnterpriseWebDAVSolution/EnterpriseWebDAV-DriveMapping.htm

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Alternatively, you can use DriveHQ FileManager 5.2 client software. The software is free and you can install it on any number of computers. It is integrated with our Cloud IT service, so you have access to more features, such as: Drag & Drop; Sharing & Collaboration; Folder & File Publishing; Edit & Save Back; Local File Caching; Automatic Folder Synchronization; Encrypted Folder; File Versioning; Data Compression; Resuming Interrupted Uploads / Downloads, Bandwidth Throttling, etc.