Why can't some salts be used in the salt bridge of specific voltaic cells?

I had an exam question in reference to a galvanic cell with $\ce{Pb{(s)}}$ as the anode in $\ce{Pb^2+}$ solution and platinum cathode in a solution of $\ce{Fe^2+}$ and $\ce{Fe^3+}$:

Identify an appropriate electrolyte to use in the salt bridge.

I gave $\ce{KNO3}$ which was correct. However, the marking criteria specified that sulphate and chloride salts were not usable.

Why are these salts not usable? Is there any way to tell which salts would be usable for other galvanic cells?