The email address you have entered does not contain an "@" symbol. Valid e-mail addresses should be of the form username@hostname.domain.
The email address you have entered contains a colon or semicolon, which are not legal characters for an e-mail address. If your address is for a Compuserve account, leave off the "INTERNET:" prefix.
This e-mail address is not valid because it contains a comma. If you have a CompuServe account such as 99999,999@compuserve.com, replace the comma with a period: 99999.999@compuserve.com.
Your email address contains a space. Spaces are not allowed inside e-mail addresses.
The email address you have entered is not of the form username@hostname.domain. The period is improperly placed -- either at the beginning or end of the address, or immediately before the "@" symbol.
E-Mail Address field cannot be blank.
The email address you have entered is not of the form username@hostname.domain. The "@" symbol is either improperly placed (it is not allowed at the beginning or end of the address), is missing entirely, or appears multiple times in the address.
The email address you have entered is not of the form username@hostname.domain. The host and domain part of your email address (e.g., @realaudio.com) must contain at least two words, connected by a period.