Unknown argument for ':' operator. Complete Regular Expression required in search string.
This error generally occurs during search or replace when regular expressions or wildcards are used in a search string. The operator colon (:) was entered but the argument that followed was not a valid argument.
Note
Arguments for the colon (:) operator are case-sensitive.
To correct this error
Review the correct regular expression syntax located in the topic "Regular Expressions."
Double-check that the correct case of the argument was used.
If you are using an Input Method Editor (IME), make sure that the argument is not given using full-width characters.
See Also
Reference
Regular Expressions (Visual Studio)