Html.TextBoxFor(txtProjRev_1 => Model.txtProjRev_1, new { @class = "textboxyear", onkeypress = "javascript:checkval(this);" })
should be
Html.TextBoxFor(m => m.txtProjRev_1, new { @class = "textboxyear", onkeypress = "javascript:checkval(this);" })
You'll have to update that for any reference like this.