Melt the butter in a heavy 4-quart saucepan over low heat.
Using a rubber spatula, bring it up around the sides of the pan to grease it well.
Add the sugar, corn syrup, cream, water, and salt.
Cook over low heat, stirring constantly, until the sugar is dissolved.
Continue cooking over medium heat, stirring occasionally, to 238°, or until a little of the syrup dropped into cold water forms a soft ball.
Remove from the heat and allow to cool, without disturbing, until lukewarm (110°).
Blend in the marshmailow creme and vanilla.
Beat until the mixture loses its gloss and starts to thicken.
Quickly stir in the cherries and pecans; then spread the mixture into an even layer in a lightly buttered 9 x 12 x 2-inch pan.
Cool until firm, then cut into squares.