why asp.net autocompleteextender returning undefined?

why am i removing textbox advantage capricious list variables?

when i run code:

var query = (from tisa db.ta_info_step_archives
                 where tisa.ta_serial.tostring().startswith(prefixtext)
                 name tisa.ta_serial.tostring()).distinct().take(convert.toint32(count));

return query.tolist<string>().toarray();

i xml file:

<string>200700160</string> 
  <string>200700161</string> 
  <string>200700162</string> 
  <string>200700163</string> 
  <string>200700164</string> 
  <string>200700170</string> 
  <string>200700171</string> 
  <string>200700172</string> 
  <string>200700173</string> 
  <string>200700174</string> 
  <string>200700175</string> 
  <string>200700176</string> 
  <string>200700177</string> 
  <string>200700178</string> 
  <string>200700179</string> 
  <string>200700180</string> 
  <string>200700181</string> 
  <string>200700182</string> 
  <string>200700183</string> 
  <string>200700184</string> 

but, textbox advantage list undefined....

help please?