Facing this error while Acquia Drupal set up
Not much info so this is a bit of a guess...

Acquia support PHP versions:


  5.3.29, 5.4.45, 5.5.30 (default), 5.6.14, 7.0.0 RC2


The error message you're seeing suggests short array syntax isn't understood by the version of PHP that's running, which in turn suggests you're running the 5.3.29 option.

Short array syntax was added in PHP5.4, so in theory to fix you just need to install the software with that version instead of 5.3.