Windows XP Visual C++ Link Error LNK2028 & LNK2019

[SteveClarke]

Hi,
I am writing my first windows application and trying to call some code on a button press. I get the following errors when linking.

test.obj : error LNK2028: unresolved token (0A000019) "public: void __clrcall Test_IO::Open(void)" ((e-mail address removed)) referenced in function "void __clrcall B_Pressed(void)" (?B_Pressed@@$$FYMXXZ)

test.obj : error LNK2019: unresolved external symbol "public: void __clrcall Test_IO::Open(void)" ((e-mail address removed)) referenced in function "void __clrcall B_Pressed(void)" ((e-mail address removed))

Any ideas how to get it linking?

Thanks
Steve