Why is the index of the vector in the last loop of the merge program going out of range?

<pre>#pragma once
#include <vector>

template<typename T>
void MergeSort(std::vector<T>& vArray, std::vector<T>& vHelper, size_t iLow, size_t iHigh);

template<typename T>
void Merge(std::vector<T>& vArray, std::vector<T>& vHelper, size_t iLow, size_t iMiddle, size_t iHigh);

template<typename T>
void MergeSort(std::vector<T> &vArray)
{
	std::vector<T> vHelper(vArray.size());
	MergeSort(vArray, vHelper, 0, vArray.size() - 1);
}

template<typename T>
void MergeSort(std::vector<T> &vArray,std::vector<T> &vHelper,size_t iLow,size_t iHigh)
{
	if(iLow < iHigh)
	{
		size_t iMiddle = (iLow + iHigh) / 2;

		MergeSort(vArray,vHelper, iLow, iMiddle);//sort left half
		MergeSort(vArray,vHelper, iMiddle + 1, iHigh);//sort right half
		Merge(vArray, vHelper, iLow, iMiddle, iHigh);//merger both halves
	}
}

template<typename T>
void Merge(std::vector<T>& vArray, std::vector<T>& vHelper, size_t iLow, size_t iMiddle, size_t iHigh)
{
	//copy both halves into the helper array
	for (size_t i = iLow; i <= iHigh; i++)
	{
		vHelper[i] = vArray[i];
	}

	size_t iHelperLeft = iLow;
	size_t iHelperRight = iMiddle + 1;
	size_t iCurrent = iLow;

	/*Iterate throght helper array. 
	Compaeres the left half to the right half and copy back the smaller element into the original array*/

	while (iHelperLeft <= iMiddle && iHelperRight <= iHigh)
	{
		if (vHelper[iHelperLeft] < vHelper[iHelperRight])
		{
			vArray[iCurrent] = vHelper[iHelperLeft];
			iHelperLeft++;
		}
		else
		{
			vArray[iCurrent] = vHelper[iHelperRight];
			iHelperRight++;
		}
		iCurrent++;
	}

	//copy the remaining of the left sideof the helper array
	size_t iRemaining = iMiddle - iHelperLeft;

	
	for (size_t i = 0; i <= iRemaining; i++)
	{
		
		
		vArray[iCurrent + i] = vHelper[iHelperLeft + i];//one of these vectors go out of range
	}

}