Nothing is wrong with your system, you're just using the wrong path to env. On Linux systems, at least, the env binary is normally in /usr/bin and not /bin:
$ type env env is /usr/bin/env So, your script is telling your system to use /bin/env, which doesn't exist, and that's why you're getting that error. Simply change to the right shebang and you should be fine:
#!/usr/bin/env bash