diff --git a/lib/spack/spack/solver/asp.py b/lib/spack/spack/solver/asp.py
index 0e60e94d7de..cccadf40fea 100644
--- a/lib/spack/spack/solver/asp.py
+++ b/lib/spack/spack/solver/asp.py
@@ -614,7 +614,7 @@ def multiple_values_error(self, attribute, pkg):
     def no_value_error(self, attribute, pkg):
         return f'Cannot select a single "{attribute}" for package "{pkg}"'
 
-    def _get_cause_tree(self, cause, conditions, condition_causes, literals, indent=""):
+    def _get_cause_tree(self, cause, conditions, condition_causes, literals, indent="        "):
         parents = [c for e, c in condition_causes if e == cause]
         local = "required because %s " % conditions[cause]
 
@@ -626,9 +626,9 @@ def _get_cause_tree(self, cause, conditions, condition_causes, literals, indent=
             )
         ]
 
-    def get_cause_tree(self, result, best_model, cause):
-        conditions = dict(extract_args(best_model, "condition"))
-        condition_causes = list(extract_args(best_model, "condition_cause"))
+    def get_cause_tree(self, cause):
+        conditions = dict(extract_args(self.model, "condition"))
+        condition_causes = list(extract_args(self.model, "condition_cause"))
         return self._get_cause_tree(cause, conditions, condition_causes, [])
 
     def handle_error(self, msg, *args):
diff --git a/lib/spack/spack/solver/causation.lp b/lib/spack/spack/solver/causation.lp
index 9324f0d4587..626bfcf8f03 100644
--- a/lib/spack/spack/solver/causation.lp
+++ b/lib/spack/spack/solver/causation.lp
@@ -64,9 +64,9 @@ error(0, "Version '{0}' of {1} does not satisfy '@{2}'", Version, Virtual, Const
 
 % More specific error message if the version cannot satisfy some constraint
 % Otherwise covered by `no_version_error` and `versions_conflict_error`.
-error(0, "No valid version for '{0}' satisfies '@{1}'", Package, Constraint, startcauses, ConstraintCause)
+error(0, "Cannot satisfy '{0}@{1}'", Package, Constraint, startcauses, ConstraintCause)
   :- attr("node_version_satisfies", Package, Constraint),
      imposed_constraint(ConstraintCause, "node_version_satisfies", Package, Constraint),
      condition_holds(ConstraintCause),
-     C = #count{ Version : attr("version", Package, Version), version_satisfies(Package, Constraint, Version)},
-     C < 1.
+     attr("version", Package, Version),
+     not version_satisfies(Package, Constraint, Version).