Reason: This occurs when the DISPLAY variable is not set.
Solution 1: If you are installing the product in a non-GUI environment, execute the bin file as given below:
./ManageEngine_ApplicationsManager.bin -console
Solution 2: If you are installing the product in a GUI environment, set the DISPLAY variable and then install the product.
Example:
export DISPLAY=localhost:0.0 [To set the DISPLAY variable]
xhost + [To provide permission for the remote hosts to open the GUI]
./ManageEngine_ApplicationsManager.bin