The error means that the columns you are trying to join on are not the same data type. You must ensure they are the same type.
So as you have said it is the second join causing the problem, then that means that the following columns are different data types.
SapDumpFeb.GL_AC_NO
GlText.GL_AC_NO
Check these and make sure they match.
Alternatively, if you can't change the type you may be able to convert one of them in the join. For example, if one is a string you can convert the other to string in the join:
join g in dbContext.GlTexts on Convert.ToString(s.GL_AC_NO) equals g.GL_AC_NO