Metasploit Exploitation Question

I tried doing a metasploit exploitation using a payload created with veil-evasion. This payload worked with other computers in my own network and with the computer of a friend of mine. Nevertheless it didn't work when I tested it with computer science with permission of the teacher.

• I made the payload with Veil-Evasion.
• payload: python/shellcodeinject/base64substitution
• extension is .exe
• IP= public IP
• Port = forwarded
• School might be using their own server?
• I tried pinging the IP of the target and it responds well.

This is what I get:

but no meterpreter sessions is started.

Does anyone know how to solve this?