Shader compile Texture coordonates issue

When I compile one of my shader, I get this error:

// Too many texture interpolators would be used for ForwardBase pass:
// no lightmaps:
#ifdef LIGHTMAP_OFF
struct v2f_surf {
float4 pos : SV_POSITION;
fixed3 worldNormal : TEXCOORD0;
float3 worldPos : TEXCOORD1;
float4 custompack0 : TEXCOORD2; // bumpTexCoord
half3 custompack1 : TEXCOORD3; // objSpaceNormal
half3 custompack2 : TEXCOORD4; // viewVector
float4 custompack3 : TEXCOORD5; // grabPassPos
float4 custompack4 : TEXCOORD6; // offset
float4 lmap : TEXCOORD7;
fixed3 vlight : TEXCOORD8; // ambient/SH/vertexlights
SHADOW_COORDS(9)
UNITY_FOG_COORDS(10)
};
​

Because it is a transparent shader, I don't see why Unity adds:
SHADOW_COORDS(9)
Also what is float4 lmap : TEXCOORD7; actually?

Is there a way to control these texcoords in order to optimize a shader?
For example with U5, in target 3.0, I have only 3 Textcord left, 7 are used by Unity.
With Unity 4, the same shader was working fine.