The SLC-5/01 controllers have only a Data Highway 485 (DH485) network port, so you must be using some kind of DH485 driver in RSLinx Classic.
What exact physical interface are you using between your PC and the SLC-5/01 controller ?
FactoryTalk View can use RSLinx Classic as an OPC Server, but it is more common for it to use its built-in data provider, called RSLinx Enterprise.
RSLinx Enterprise and RSLinx Classic don't share the same physical hardware, so you probably have a physical resource conflict, like a serial port conflict.
When I have to use serial interfaces to SLC-5/0x controllers along with FactoryTalk View, I usually use two: one for RSLinx Classic and one for RSLinx Enterprise.