deleting a shared resource

I am having trouble with thread saftey..

I have a class A that has members
int m_count;
int m_data;
CCriticalSection m_ lock;

I have one thread that creates a single class A and sets m_count to the
number of threads it will be sending to.
as other threads are done with it, they then call the function A::remove()
which looks like:

void remove() {
    m_lock.Lock()
    if(!--m_count){
        m_lock.Unlock();
        delete this;
        return;
     }
    m_lock.Unlock();
}

is this thread safe?

I would think so because it is accessing m_count only after it achieves the
lock and can only enter the ifstatement when count == 0.

this does work for a minimal number of threads, about 10. however 10+, the
program hangs, cpu usage goes to 100% (assuming its a spin lock) and after a
while(~15 seconds) I get the error:

Unhandled exception at 0x7c91b1fa in canANALYZERBackend.exe: 0xC0000005:
Access violation writing location 0x0000001a.

and breaks at line 81 in afxmt.inl