Reading Block of elements from dataset containing opaque data type

Hi all,

I have a dataset where each element is defined by this struct

struct data
  unsigned short value;
  char buf[500];

A compound datatype is defined with one subtype being native unsigned short
and other being opaque ( H5T_OPAQUE of length 500) .

I am able to select a single element and do a H5Dread but i am not able to
read a block of elements . A block read only reads the first element in the
dataset .

    the number of elements in the dataset is 12 for the use case i am

    data* d1= new data[numOfElements];
    for(size_t i=0; i<numOfElements; ++i)
        dspace = H5Dget_space(dataset);
        //status = H5Sselect_all(dspace);
        //! Select the dataspace to which the information has to be read
        status = H5Sselect_elements(dspace, H5S_SELECT_SET, 1, offset) ;
        status = H5Dread(dataset, type, memspace, dspace, H5P_DEFAULT,

but this doesn't work
    //cord is a 1d array with values from 0 to 11.
    status = H5Sselect_elements(dspace, H5S_SELECT_SET, 12, coord) ;
    status = H5Dread(dataset, type, memspace, dspace, H5P_DEFAULT, &d1[0]);

neither this works
    hsize_t start=0;
    hsize_t stride=1;
    hsize_t count = 12;
    hsize_t block=1;
    status = H5Sselect_hyperslab(dspace, H5S_SELECT_SET, offset, &stride,
&count,&block );
    status = H5Dread(dataset, type, memspace, dspace, H5P_DEFAULT, &d1[0]);

I only get the correct value for d1[0[] - d1[1] to d1[11] are garbage
values .
There is no error returned by H5Dread .

Any suggestions as to how can the entire dataset be read in one read ?