Hello Tahaseen,
If the Special character "@" is not to be considered in the complete DME fields, use the "character defination"
field in DME tree Properties (File data tab) - as also mentioned by others. Enter the Special character "@" and select the Option "do not allow These characters".
However, if teh Special character Need not to be considered only for this particular node, then make use of "source Offset" field in the source tab (set it as 1 so that the 1st character is ignored from the field value).
Hope that helps
BR
Amitash