I was wondering if its actually possible to do bump mapping with 2 normal maps... I have tried doing it this way however I get a function overload on max and dot.

uniform sampler2D  n_mapTex;
uniform sampler2D  n_mapTex2;
uniform sampler2D  refTex;

varying mediump vec2  TexCoord;
varying mediump float vTime;

void main()
{   
    mediump vec4 wave = texture2D(n_mapTex, TexCoord - vTime);
    mediump vec4 wave2 = texture2D(n_mapTex2, TexCoord + vTime);
    mediump vec4 bump = mix(wave2, wave, 0.5);
    //this extracts the normals from the combined normal maps
    mediump vec4 normal = normalize(bump.xyzw * 2.0 - 1.0);
    //determines light position
    mediump vec3 lightPos = normalize(vec3(0.0, 1.0, 3.0));

    mediump float diffuse = max(dot(normal, lightPos),0.0);
    gl_FragColor = mix(texture2D(refTex, TexCoord), bump, 0.5);
}