BLD:W0018
Expression "%s" contains a character '%c' that is not allowed in file names
The indicated expression contains one or more characters that are not allowed in a file name. Although the expression expansion will succeed, the resulting value might not be valid for the context in which it is used and may cause the installation to fail.
For example, a shortcut's title must also be a valid file name, because the title is used as a file name when the shortcut is created and invalid characters will cause the shortcut creation to fail.
The following characters are not allowed in a file name:
"\/:|<>*?
Note that '<' and '>' are allowed if they delimit symbolic variable references. In that case, they are removed when the expression is expanded and the references are resolved.
Solution
You should check the indicated expression and characters that are not allowed in a file name. Note that the offending characters may occur in the expansion of expression rather than in expression itself. For example, if this message refers to the title of a shortcut that is set to <ProductName> and the ProductName variable is set to *Ultrasoft*, then the '*' in ProductName are the real culprits.