The following error message is displayed when logging on to NetScaler GUI after an upgrade:
Login command failed over API. Reason: Response not of type text/xml: text/html

Solution 1 - Does not keep the customization

1. Log on through NetScaler Command Line Interface and run the following command:
   >show vpn parameter 
   This will show which UI theme is applied currently (DEFAULT/CUSTOM/GREEN BUBBLE).

2. If a custom theme is applied then change it to default theme by running the following command:
   > set vpn parameter -UITHEME DEFAULT

3. Save the config.

Solution 2 - Keeps the customization

1. Downgrade NetScaler to the old version.

2. Perform a backup of the custom folder.

3. Remove the customizations before upgrading.

4. Upgrade and then apply the customization.

Problem Cause

Customizations should not be included and should be removed prior to upgrade.