Here are three choices for you:
Easiest fix is to get rid of the Conversion class and write specialized versions of getValueOfKey.
Alternative 2: make Conversion a template class (instead of a class with template members).
template <typename T> class Conversion {
Alternative 3: make Conversion a namespace.
<pre>namespace Conversion {
Additional comments:
Value, Key, Whitespace, deleteComments, and validLine can be static instead of const member functions.