Then you need to upgrade php version or fix the code related to the line 175 (and what’s exactly you have there? - actual code usually clarifies the situation).
Most probably you have something like
::$var
. Usage of $var in this case causes the error. Try to replace it, if possible with method/property name.
I don’t know which versions of php are supported by Zurmo. If they officially support versions <5.3, then you should report them about the problem.