Problem with heap

Can any body tell me what is wrong with the program
program perform well but messup after finishing
GlobalFree(tData);
Some one please give me a solution

Code:

#include <math.h>
#include <windows.h>
#include <stdio.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <io.h>
#include <stdlib.h>
#include <errno.h>
#include <share.h>
#include <io.h>
#include <sys/locking.h>
#include <share.h>
#include <string.h>

int base64(char src[4], int bytes, char ret[4]);
void Base64(wchar_t SourceFileName[500],wchar_t DestinationFileName);

char text[64]="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

void main()
{	
	Base64(TEXT("E:\\c7.bmp"),TEXT("E:\\OUTPUT.txt"));
}

void Base64(wchar_t SourceFileName[500],wchar_t DestinationFileName[500])
{
	int SourceFile;
	int DestinationFile;
	int data;
	char *tData;
	int bytesWritten;
	int bytesRead;
	DWORD err;
	char *b64;
	int towrite;
	int count;
	
	b64=GlobalAlloc(GMEM_FIXED,5);
	tData=GlobalAlloc(GMEM_FIXED,4);
	SourceFile = _wsopen(SourceFileName,_O_RDONLY|_O_BINARY,_SH_DENYWR,_S_IREAD);	
	if(EACCES==SourceFile)
		printf("Given path is a directory, or file is read-only, but an open-for-writing operation was attempted.\n");
	else if(EEXIST==SourceFile)
		printf("_O_CREAT and _O_EXCL flags were specified, but filename already exists.\b");
	else if(EINVAL==SourceFile)
		printf("Invalid oflag or shflag argument.\n");
	else if(EMFILE==SourceFile)
		printf("No more file descriptors available.\n");
	else if(ENOENT==SourceFile)
		printf("File or path not found.\n");
	DestinationFile=_wsopen(DestinationFileName,_O_CREAT|_O_BINARY|_O_RDWR,_SH_DENYWR,_S_IREAD|S_IWRITE);		
	if(EACCES==DestinationFile)	
		printf("Given path is a directory, or file is read-only, but an open-for-writing operation was attempted.\n");
	else if(EEXIST==DestinationFile)
		printf("_O_CREAT and _O_EXCL flags were specified, but filename already exists.\b");
	else if(EINVAL==DestinationFile)
		printf("Invalid oflag or shflag argument.\n");
	else if(EMFILE==DestinationFile)
		printf("No more file descriptors available.\n");
	else if(ENOENT==DestinationFile)
		printf("File or path not found.\n");
	
	err=GetLastError();
	if (err==ERROR_ALREADY_EXISTS)
	{
		_close(DestinationFile);
		DeleteFile(DestinationFileName);
		DestinationFile=_wsopen(DestinationFileName,_O_CREAT|_O_BINARY|_O_RDWR,_SH_DENYWR,_S_IREAD|S_IWRITE);
	}

	count = 0;
	while((bytesRead=_read(SourceFile,tData,3))==3)
	{	
		tData[4]=0;
		towrite=base64(tData,bytesRead,b64);
		if (( bytesWritten = _write(DestinationFile,b64,towrite)) == -1 )
		{
			switch(errno)
			{
				case EBADF:
					perror("Bad file descriptor!");
					return;
				case ENOSPC:
					perror("No space left on device!");
					return;
				case EINVAL:
					perror("Invalid parameter: buffer was NULL!");
					return;
				default:
					// An unrelated error occured 
					perror("Unexpected error!");
					return;
			}
		}
		tData[3]='\0';
		count=count+bytesWritten;
		if (count==76)
		{
			b64[0]='\n';
			b64[1]='\0';
			bytesWritten = _write(DestinationFile,b64,1);
			count = 0;
		}
	}
	if(bytesRead<3 && bytesRead>0)
	{
		towrite=base64(tData,bytesRead,b64);
		tData[0]='\0';
		if (( bytesWritten = _write(DestinationFile,b64,towrite)) == -1 )
		{
			switch(errno)
			{
				case EBADF:
					perror("Bad file descriptor!");
					break;
				case ENOSPC:
					perror("No space left on device!");
					break;
				case EINVAL:
					perror("Invalid parameter: buffer was NULL!");
					break;
				default:
					// An unrelated error occured 
					perror("Unexpected error!");
			}

		}
	}
	//_write(DestinationFile,tData,bytesRead);	
	_close(SourceFile);
	_close(DestinationFile);
	GlobalFree(b64);
	[COLOR="Red"]GlobalFree(tData);[/COLOR]
	
}

int base64(char src[4],int bytes,char ret[4])
{	
	unsigned int ConvertedINT;	
	int i,j;	
	int tmp;
	int TmpData;	

	ConvertedINT=0;
	
	for(i=bytes-1,j=0;i>=0;i--,j++)
	{
		ConvertedINT = ConvertedINT+src[i]*pow(256,j);
	}
	if(bytes==1)
	{
		ConvertedINT=ConvertedINT*16;
		TmpData=ConvertedINT;	
		tmp = TmpData/64;
		ret[0]=text[tmp];
		TmpData=TmpData-tmp*64;
		ret[1]=text[TmpData];
		ret[2]='=';
		ret[3]='=';
		ret[4]='\0';

	}
	else if(bytes==2)
	{
		ConvertedINT=ConvertedINT*4;
		TmpData=ConvertedINT;
		tmp = TmpData/4096;
		ret[0]=text[tmp];
		TmpData=TmpData-tmp*4096;
	
		tmp = TmpData/64;
		ret[1]=text[tmp];
		TmpData=TmpData-tmp*64;
		ret[2]=text[TmpData];
		ret[3]='=';
		ret[4]='\0';
	}
	else
	{
		TmpData=ConvertedINT;
		tmp=TmpData/262144;
		ret[0]=text[tmp];
		TmpData=TmpData-tmp*262144;

		tmp = TmpData/4096;
		ret[1]=text[tmp];
		TmpData=TmpData-tmp*4096;
	
		tmp = TmpData/64;
		ret[2]=text[tmp];
		TmpData=TmpData-tmp*64;
		ret[3]=text[TmpData];
		ret[4]='\0';
	}
	return strlen(ret);
}

 

OK,
I actually asked this question long time ago and nobody ans me.
But I figured the problem

The problem was I alocate 4 bytes for tData variable
tData=GlobalAlloc(GMEM_FIXED,4);
But I accessed 5th byte
tData[4]=0;
That is why the program failed to release heap. The limit is from 0 to 3