Code page 437 is the original MS-DOS character set on the PC. See http://en.wikipedia.org/wiki/Code_page_4… . In this character set, character 236 is ∞ .
But Microsoft later invented other code pages for different languages or to be more similar to the Windows code page 1252. Windows Code page 1252 covers western European languages and is the normal Windows code page installed on computers where the language is set to a form of English. The DOS code page that most closely resembles Windows code page 1252 was originally Code page 850. See http://en.wikipedia.org/wiki/Code_page_8… . In this code page character 236 has the value ý. When the Euro system € was invented, Microsoft invented yet another DOS code page which they called 858 which was identical to Code page 850, except that it included € instead of ı, the dotless i. See http://en.wikipedia.org/wiki/Code_page_8… .
You may have have different Code page installed.
I have seen some people report that adding an additional 0 to the start helps. So, you could try ALT+00120
Or, you have some mapping tool installed, like AutoHotKey or a clipboard manager which is providing undesired results.