Have you tried:
MyFile.Replace(Environment.NewLine, "")
Which on Windows should be the same as:
MyFile.Replace(vbCrLf, "")
Also try:
MyFile.Replace(vbCr, "")
or
MyFile.Replace(vbLf, "")
Depending on the type of newline you have, either should work for you.
EDIT: regarding why MyFile.Replace(10,"")
did not work for you. You became a victim of implicit type conversion (a feature of VB.NET), so this line was executed as:
MyFile.Replace("10","")
Please make sure you have Option Strict On
, if you want to avoid such issues.