nowdate changed to purchase_date

next depreciation date should be compared with purchase_date instead of nowdate.
diff --git a/erpnext/accounts/doctype/asset/asset.py b/erpnext/accounts/doctype/asset/asset.py
index 9caac07..6a0cef5 100644
--- a/erpnext/accounts/doctype/asset/asset.py
+++ b/erpnext/accounts/doctype/asset/asset.py
@@ -80,7 +80,7 @@
 			if cint(self.number_of_depreciations_booked) > cint(self.total_number_of_depreciations):
 				frappe.throw(_("Number of Depreciations Booked cannot be greater than Total Number of Depreciations"))
 						
-		if self.next_depreciation_date and getdate(self.next_depreciation_date) < getdate(nowdate()):
+		if self.next_depreciation_date and getdate(self.next_depreciation_date) < getdate(self.purchase_date):
 			frappe.msgprint(_("Next Depreciation Date is entered as past date"))
 			
 		if (flt(self.value_after_depreciation) > flt(self.expected_value_after_useful_life) 
@@ -242,4 +242,4 @@
 		"asset_category": asset_category
 	})
 		
-	return ret
\ No newline at end of file
+	return ret