error: invalid lvalue in assignment

Hello,

I'm getting this error:

../templates.hpp: In function 'Img crop(const Img&, const
cvmlcpp::iPoint2D&, const cvmlcpp::iPoint2D&) [with Img =
ili::BWImg]':
RectangleImageComparator.cc:85: instantiated from here
../templates.hpp:61: error: invalid lvalue in assignment

What's weird is that exactly the same template works with another
image type, as in the file where I instantiate it I have:

-------- begin extract RectangleImageComparator.cc -------
 84 IntImg rectImg = crop<IntImg>(tempImage, corners[0],
corners[2]); // this function instantiates correctly
 85 BWImg rectBWI = crop<BWImg>(bwImage, corners[0],
corners[2]); // if I eliminate this line (and all that uses the
result) all the code works
-------- end extract RectangleImageComparator.cc -------

The images are template classes defined like this:

typedef cvmlcpp::Matrix<bool , 2u> BWImg;
typedef cvmlcpp::Matrix<int_t, 2u> IntImg;

So, why would the instantiation work with the int version and not with
the boolean?? What does it mean the "error: invalid lvalue in
assignment", why does it appear only in the instantiation on the
boolean img??

Thanks for your help,

eD

-------- begin extract templates.hpp -------

 29 template <class Img>
 30 Img crop(const Img &img, const cvmlcpp::iPoint2D &ulc,
 31 const cvmlcpp::iPoint2D &brc)
 32 {
 33 typedef typename Img::value_type T;
 34
 35
 36 // check for valid arguments
 37 // the image itself will take care of the out of bound
exception
 38
 39 /// \todo TODO put this function in the library
 40 unsigned newHeight = ((brc[0] - ulc[0]) > 0) ? (brc[0] - ulc
[0]) : 0;
 41 unsigned newWidth = ((brc[1] - ulc[1]) > 0) ? (brc[0] - ulc
[0]) : 0;
 42
 43 if (newHeight == 0)
 44 {
 45 std::invalid_argument myException("Height");
 46 throw myException;
 47 }
 48 else if (newWidth == 0)
 49 {
 50 std::invalid_argument myException("Width");
 51 throw myException;
 52 }
 53
 54 Img myImage = ili::init<Img>(newHeight, newWidth);
 55
 56 // now we do the copying
 57 for (unsigned i = 0; i < newHeight; i++)
 58 {
 59 for (unsigned j = 0; j < newWidth; j++)
 60 {
 61 myImage[i][j] = img[ulc[0] + i][ulc[1] + j]; // this
would be the line
 62 }
 63 }
 64
 65 return myImage;
 66 }