Hello Ashnil,
It will be worth seeing what version the model you are trying to open was last saved in. You can open the .wtg file in Notepad and look for the field "ProductVersionLastModified". This link has more info on finding this information.
If it was saved in a later version from what you are using, the best solution would be to upgrade. Other options including having the user you received the model from export the model into an EPANET format and then open the EPANET file in your version of WaterGEMS. This link has information on this.
Regards,
Scott