Repeated String - Runtime error

I can’t figure out what’s wrong with my code. It works fine on my machine???

#include<stdio.h>
#include<string.h>
#define SIZE 10000
int repstring(char a[], int len )
{
char substr[20][10] ={'\0'};

int k=0,count2=0,i,j,h,count,l;
for(i=0;i<=strlen(a)-len;i++)
{
	for(j=i;j-i<len;j++)
		substr[k][j-i]=a[j];

	substr[k][j-i]='\0';

	for(h=0;h<k;h++)
	{count=1;
	for(l=h+1;l<=k;l++)
		if(strcmp(substr[h],substr[l])==0)
			count++;
	if(count>count2)
		count2=count;

	}
	k++;

}
return count2;

}

int main()

{

int count,count2,l,h,i,j;
char a[SIZE];
do
{
	scanf("%d",&l);
	scanf("%d",&h);
	if(l==0 && h==0)
		break;
	scanf("%s",&a);
	count =0;
	for (i=l;i<=h;i++)
	{
		count2=repstring(a,i);
		if(count2>count)
		{
			count=count2;
			j=i;

		}

	}

	printf("%d %d",count,j);
}while(1);
return 0;

}

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