DTD error problem

I have a customer who is trying to open an xml against a dtd and he continues to get  the error:

C:\Users\lvian\Documents\spec2200_2011.1a\DTDs\cmm.dtd : Line: 217 Column: 66

Expected quoted string

I looked at column 66, line 217 and it says this:

<!ENTITY   % ISOtech      PUBLIC

     "ISO 8879-1986//ENTITIES   General Technical//EN"           >

Looks like the string is quoted. Does anyone have any ideas on what this could be?