2.8 Winbox Tool

I have two MT V2.8.28 routers on my network. To access these with Winbox from the Dude I have created a custom tool with the following command line:

“C:\Program Files\Winbox\winbox.exe” [Device.FirstAddress]:800 [Device.UserName] [Device.Password]

For one of the routers this works fine. On the other, only the winbox loader window appears, with the correct address, username and password, and I then have to click connect to run Winbox.

Any ideas why this tool does not work the same on both routers?

Thanks.