Many fonts are available from various foundries. In many cases the design of the typeface is identical, but the naming conventions are different, which will trigger the "missing font" error.
One such common case of this is with Helvetica. A document may call for "Helvetica-Bold". You then purchase Helvetica Bold, install it, and open up the document, only to be alerted to a missing font. This is because Linotype's version of Helvetica will actually have the name "HelveticaLT-Bold", to signify that it is a Linotype font. A version without the LT in the name is likely from Adobe, which sub-licensed Helvetica for distribution long ago.
Many applications have a Find/Replace function for fonts. You should be able to replace Helvetica-Bold with HelveticaLT-Bold and not encounter any issues with your layout.