Ah, you must have PHP 5.3.x, which doesn't support the [] syntax for arrays. I've changed them to the old array() style.
https://github.com/Fabrik/fabrik/commit/d8a1f2892cfd062555bdda6f8e70124b6cd12cf2
... but I suspect that this won't help, and the new version of the TwitterOAuth library we're using won't work, as I think it uses 5.4+ syntax for arrays internally.
Regardless of this specific issue, you should seriously look at upgrading. 5.3.x is getting very old - it was "end of lifed" by PHP.org in 2014, and is no longer supported. We're currently working on PHP 7 compatibility for Joomla / Fabrik. You are going to find more and more things breaking as more coders no longer write code for such old versions.
I know this breaks our theoretical minimum PHP version of 5.3.10 (or rather, Joomla's), but the recommended minimum for J! is 5.6. And this TwitterOAuth lib is the only game in town, so we don't have much choice but to use it.
Actually, someone just pointed out to me that Akeeba have just said they are going to be dropping support for 5.3 ... this is from their latest release notes ...
"Please note that PHP 5.3 is obsolete since August 2014 and we're going to stop supporting it without warning in future versions of our software"
... so if you use Akeeba to backup, upgrading PHP is going to be a necessity.
-- hugh