Question: Issue with "Compiler:-Compile"

For each of the definitions

p := proc( x :: float ) :: float; x^(2/3) end proc:
p := proc( x :: float ) :: float; x^evalf((2/3)) end proc:

i get an error by calling Compiler:-Compile( p ):

"Error, (in printtab[CodeGeneration:-Names:-Rational])
rational numbers and arithmetic are not yet supported"

Any suggestions what to do (except manually converting
all exponents to floats)?

Edited to add: for example the following does not work:

c := proc (S::float, K::float, t::float, r::float, v::float)::float; 
S*(1/2+1/2*erf(1/2*((ln(S/K)+r*t)/v/t^(1/2)+1/2*v*t^(1/2))*2^(1/2)))-
K*exp(-r*t)*(1/2+1/2*erf(1/2*((ln(S/K)+r*t)/v/t^(1/2)-1/2*v*t^(1/2))*2^(1/2))) 
end proc;

Compiler:-Compile( c ); # gives the same error message  :-(