exc_bad_access when using VBO's in Cocos2d - iphone

Question

In my iPhone application I am creating a vertex buffer as shown below:
-(id)initWithPoints:(NSArray *)polygonPoints andTexture: (CCTexture2D *) fillTexture{
self = [super init];
if(self){
int vertexCount = [polygonPoints count];
CGPoint *vertices = (CGPoint*)malloc(sizeof(CGPoint)*vertexCount);
GLushort *indices = (GLushort*)malloc(sizeof(GLushort)*2*vertexCount);
int i = 0;
for(NSValue *value in polygonPoints){
CGPoint p = [value CGPointValue];
vertices[i] = ccp(p.x, p.y);
i++;
}
for (int k = 0; k<vertexCount; k++) {
indices[k] = (GLushort)k;
}
NSLog(#"count: %i", vertexCount);
glGenBuffers(1, &vertexBuffer);
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
glBufferData(GL_ARRAY_BUFFER, vertexCount*sizeof(CGPoint), &vertices[0], GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);
glGenBuffers(1, &indexBuffer);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, (vertexCount)*2*sizeof(GLushort), &indices[0], GL_STATIC_DRAW);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
self.text = fillTexture;
}
return self;
}
And I draw it using:
-(void)draw{
glBindTexture(GL_TEXTURE_2D, self.text.name);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer);
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
glVertexPointer(2, GL_FLOAT, sizeof(CGPoint), 0);
glEnableClientState(GL_VERTEX_ARRAY);
glDrawElements(GL_TRIANGLES, 1024, GL_UNSIGNED_SHORT, 0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
}
However, I can only call glDrawElements with 1024 elements (out of ~20,000) and they render ok.
If I set it to (for example) 1025, the application crashes with EXC_BAD_ACCESS.
Obviously there's a reason the app crashes at 1024 elements, but I can't understand what it is. Any ideas would be much appreciated!