Math Times Pro 2 and Txfontsb

It is because both the packages define the command \Bbbk. mtpro2 does this:

\newcommand{\Bbbk}{\mathbb{k}}

while txfontsb the following:

\re@DeclareMathSymbol{\Bbbk}{\mathord}{AMSb}{"7C}

You can get rid of this by either undefining one of them like:

 \usepackage{txfontsb}
 \let\Bbbk\relax
 \usepackage[lite]{mtpro2}

In case if you want to use both of them, then you can copy the definition of one of them

 \usepackage{txfontsb}
 \let\myBbbk\Bbbk
 \let\Bbbk\relax
 \usepackage[lite]{mtpro2}

Then the Bbbk defined by txfontsb will be available as \myBbbk.

This is untested as I don't have mtpro2.

Related