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Step 1:

Open your file explorer (folder icon) and type %appdata% in the top navigation bar.

Step 2:

From here click on and rename the Rubex folder to RubexOLD.   This can be done by right-clicking the Rubex Folder and selecting Rename.

Step 3:
Open the Rubex application. It will treat Rubex like it was installed for the first time. Select the relevant server when it gets to this screen. This is based off of your location. 

•  Since I live in the United States I would select Option 1 to ‘Connect to the US hosted Rubex (Cloud)’