Over the last few years there has been an emerging interest in ultrawideband (UWB) communications in wireless sensor networks, mainly due to their low-complexity and low-power consumption. In particular, auto-correlation receiver (AcR) is a potential candidate for such applications. However, the presence of network interference, especially interference between uncoordinated UWB networks, will severely degrade the performance of such receiver. In this paper, we analyze the bit error probability performance of the AcR in the presence of UWB interference. We model the network interference as an aggregate UWB interference, generated by elements of uncoordinated UWB networks scattered according to a spatial Poisson process. Our analytical framework allows a tractable performance analysis and still provides sufficient insight into the effect of uncoordinated network interference on UWB systems.