First step in debugging workflow code is to comment out the "On Error" statements. If an error is being raised, those statements cause the error message to not be shown, and processing to continue with the next line.
If you comment out those statements you should see an error raised on the line:
If len(BugFields.Field(FieldName).Value)>0 then
because you have a typo in that line. "BugFields" needs to be "Bug_Fields"
If you comment out those statements you should see an error raised on the line:
If len(BugFields.Field(FieldName).Value)>0 then
because you have a typo in that line. "BugFields" needs to be "Bug_Fields"