Can I EnterCriticalSection(s) in thread A then LeaveCriticalSection(s) in thread B?

So i have SEND_SLOT struct:

struct SEND_SLOT
{
    SEND_BUFFER buffer;
    uint16 index;
    CRITICAL_SECTION slotLock;
};

and a connexion struct:

struct connexion
{
    ...
    SEND_SLOT sendSlots[3];
    ...
}

and in thread A i do:

if(TryEnterCriticalSection(&sendSlots[i]))
{  //Post send request...
   WSASend(...);
}

and in thread B i do:

while(...)
{
   ...
   //request finished, data sent, and i get the index to the SEND_SLOT
   LeaveCriticalSection(&sendSlots[index]);
   ...
}

So i'm trying to lock the SEND_SLOT i in thread A and later i want to unlock it, maybe from and other thread, but its not working, each time i try to post new send it locks the first slot even if it hash already been locked and no LeaveCriticalSection has been issued. WHY?