powershell problem when running on a remote server - access is denied
The account being local Administrator is a requirement for using the Enter-PSSession:


  To connect to a remote computer, you must be a member of the Administrators group on the remote computer.


As far as workarounds, I did find this answer on SU. I would read the article in detail that the answer points to fully understand, but this is the main command to adjust permissions:


  If you decide you want to allow others, what you do is run the
  command: 


Set-PSSessionConfiguration -Name Microsoft.PowerShell -showSecurityDescriptorUI 



  Notice that this action could have a serious impact on your system so
  we ask you to confirm that you really want to do this.