Z_DATA_ERROR ,Windows Programming

Hi Experts

                      I am using Zlib for compressing of my data. It is giving the Z_DATA_ERROR every time.I am not able to figure out the reason for this. Please let me know where I am doing wrong the source code is given below:

bBuffcompress= new BYTE[12*1024*1024];
bBuffUncompress      = new BYTE[12*1024*1024];
DWORD dwUncompressSize =12*1024*1024;
do
{
        DWORD  dwByteRead = 0;
       memset(&drCluChunk,0x00,sizeof(drCluChunk));
       ReadFile(hBackupFile, &drCluChunk, sizeof(drCluChunk),&dwByteRead,NULL);
       dwtotelbyteRead = dwtotelbyteRead + dwByteRead;
       if(drCluChunk.dwTotalCluster != 0)
      {
      DWORD mFTclusteinfile = OnResetClusterLocation(m_BackupParameter._dwRootStartCluster);
      DWORD dwCurrentFilePosition;  
      dwCurrentFilePosition = SetFilePointer(hBackupFile,0,NULL,FILE_CURRENT);
      if(drCluChunk.dwClusterStartFrom == 0)
      {
            //Partition boot record
            DWORD dw =0;
            LARGE_INTEGER      lrMovePos ={0},
            lrCurrentPos ={0};
            lrMovePos.QuadPart = 7;
            SetFilePointerEx(hBackupFile,lrMovePos ,&lrCurrentPos, FILE_CURRENT);
            memset(&ntfsHeader,0x00,sizeof(ntfsHeader));
            BYTE *Buffer = new BYTE[SECTSIZE];
            ReadFile(hBackupFile,Buffer,SECTSIZE,&dw,NULL);      
            memcpy(&ntfsHeader,Buffer,sizeof(ntfsHeader));
            LARGE_INTEGER      lrMovePos1 ={0},
            lrCurrentPos1 ={0};
            lrMovePos1.QuadPart = dwCurrentFilePosition;
            SetFilePointerEx(hBackupFile,lrMovePos1,&lrCurrentPos1,FILE_BEGIN);

      }
             if(mFTclusteinfile !=0)
      {
            DWORD dwReturnValue = 0;
            DWORD comprssbuffsize = 0;
            LARGE_INTEGER      lrMovePos ={0},
            lrCurrentPos ={0};
            lrMovePos.QuadPart = mFTclusteinfile;
            SetFilePointerEx(hBackupFile,lrMovePos ,&lrCurrentPos, FILE_CURRENT);
            bBuffcompress      = new BYTE[drCluChunk.dwCompressSize];
         ReadFile(hBackupFile,bBuffcompress,drCluChunk.dwCompressSize,&dwReturnValue,NULL);
int nFlag = uncompress(bBuffUncompress,&dwUncompressSize,bBuffcompress,drCluChunk.dwCompressSize);
}


nFlag gives (-3) the Z_DATA_ERROR.


PLease help me out  I am stuck here.