I have a 3 classes with realtionship of Base->CORD2C->CORD2R.

class TypeBase
{
private:
bool shortFormat;
string entireLine;
long fieldWidth;
public:
void setFieldWidth(string &);
void toString();
string TypeBase::mergeLines(list<string> &);
string name;
static const long MAXLINELENGTH = 80;
static const long BLANKSPACE = -99999;
friend class TypeCORD2C;
friend class TypeCORD2R;
};

Cord2c constructor takes a string and puts the numbers in its proper variable.
class TypeCORD2C: public TypeBase
{
public:
long CID;
long RID;
float A[3];
float B[3];
float C[3];
TypeCORD2C(string &);
friend class TypeCORD2R;
};

class TypeCORD2R: public TypeCORD2C
{
public:
TypeCORD2R(string &);
};

CORD2R is exactly the same as CORD2C so all initilzation are done by the parent. Is this the right way to write this child constructor?
TypeCORD2R::TypeCORD2R(string & data):TypeCORD2C(data)
{
//no code needed, all work done by parent
}

the problem occurs when I get to this line in my code:

vector<TypeCORD2R>::iterator itrCORD2R = unique(masterCORD2R.begin(),masterCORD2R.end());

compiler complains and gives me:

error C2440: 'initializing' : cannot convert from 'std::vector<_Ty>::iterator' to 'std::vector<_Ty>::iterator'
with
[
_Ty=TypeCORD2C
]
and
[
_Ty=TypeCORD2R
]
No constructor could take the source type, or constructor overload resolution was ambiguous

am I missing some constructor?