ERROR: Invalid fix style (modify.cpp:724)

I bet you misspelled something :-) A fix has everytime 4+n values:
fix ID GROUP name/of/the/fix EVERY more values
e.g.

fix 1 all nve/sphere
fix 2 all gravity 9.81 vector 0.0 0.0 -1.0

fix with id 1, group all, type nve-integrator, no every value, no additional parameter
fix with id 2 group all type gravity, no every value, additional parameters: magnitude und direction of gravity

Have a look in the logfile where the parser stops, look up the fix it was stuck in the manual and compare to an example where this fix is used.