Repeater causing signal drop

I have a problem that hopefully a network pro can solve. I recently employed a wireless router as a repeater to a main router in another house (roughly 300 feet away). It receives signal and passes it on fine. However, for some reason whenever it is on, it blocks access from the users in the main house (with the primary router). They aren't able to even connect, for the most part. However, on occasion one person can connect, but connection is spotty. Conversely, the signal coming from the repeater in the second house is very consistent...

After much testing, the cause is definitely the wireless repeater... if I unplug it, everyone can sign on in the main house without a problem. What this has resulted in is me having to leave the repeater unplugged until everyone goes to bed (or leaves) in the main house...

So, after some searching with no answers, I thought it was time to take the energy to ask the community how to solve this...

I think the problem is connected to this somehow: The repeater seems to think it IS the primary router. It has the same SSID, uses the same password, etc. I cannot access it's web configuration utility while it is repeating... it becomes locked, as if I am trying to access the main router's configuration... which, since they are both set to use the same IP address, may be the case...

I'm not going to post all the specific settings now - I'm writing this message from another location, and haven't memorized every setting of my router. Let me know what particulars you need to know about the current configuration... there are too many variables to list them all. I'm hoping someone will recognize this problem and know what it is without needing to sort through the specs...

You should be using different radio channels, check that.

A repeater reduces bandwidth, which is a greater issue at a significant distance from the main router, any chance you can run a CAT 5e cable and configure as a wireless AP instead of as a repeater?