This gives a syntax error in pdflatex. I guess I am missing a package, but I cannot think which one it is. I have installed every package I can think of ....
Up to LaTeX release 2015/01/01, an input such as
wouldn't have produced an error, but the
+ would have done nothing at all.
Starting from that release, illegal characters in the optional argument to a float environment (
figure or others defined by additional packages) produce an error
Unknown float option `<opt>'
in your case
Unknown float option `+'
Note that the only legal characters are
h t b p !
float package, one can use
H (alone), but it's not recommended.