I cannot connect a hotel Wi-Fi from my iMac air. It says problem occurred. I can join my home WiFi perfectly fine but I have issues when trying to connect the hotel Wi-Fi.

You can try these steps to connect to the hotel WiFi:

1. Click on Apple Menu > System Preferences > Network > Advanced > Navigate to the DNS tab.
2. Delete any DNS addresses that you were using under the list of DNS servers, so that it now points only to the hotel server.
3. Click OK and reload the page. The sign-in page of the public WiFi should appear. Fill out your details if required. Once you Sign-in, you should be OK to browse the internet.

Do you see any specific error messages when trying to connect to the hotel's Internet?

Most hotels use a "captive portal" which you would log into first. Typically, the access credentials are provided to your by the hotel's staff. Once successfully logged in, it should provide you with Internet access. Sometimes hotels limit this service for only a single device.