Index: includes/theme.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/theme.inc,v
retrieving revision 1.582
diff -u -p -r1.582 theme.inc
--- includes/theme.inc	4 Mar 2010 09:03:08 -0000	1.582
+++ includes/theme.inc	7 Mar 2010 01:24:52 -0000
@@ -1230,16 +1230,20 @@ function theme_render_template($template
  *   An array of theme names.
  */
 function theme_enable($theme_list) {
-  drupal_clear_css_cache();
-
+  $result = 0;
   foreach ($theme_list as $key) {
-    db_update('system')
+    $result += db_update('system')
       ->fields(array('status' => 1))
       ->condition('type', 'theme')
       ->condition('name', $key)
       ->execute();
   }
+  if (!$result) {
+    //early return if we didn't actually enable any theme
+    return FALSE;
+  }
 
+  drupal_clear_css_cache();
   list_themes(TRUE);
   menu_rebuild();
   drupal_theme_rebuild();
@@ -1252,7 +1256,7 @@ function theme_enable($theme_list) {
   // Invoke hook_themes_enabled after the themes have been enabled.
   module_invoke_all('themes_enabled', $theme_list);
 
-  return;
+  return TRUE;
 }
 
 /**
Index: includes/update.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/update.inc,v
retrieving revision 1.38
diff -u -p -r1.38 update.inc
--- includes/update.inc	25 Feb 2010 09:42:39 -0000	1.38
+++ includes/update.inc	7 Mar 2010 01:24:52 -0000
@@ -37,7 +37,7 @@ function update_check_incompatibility($n
   // Store values of expensive functions for future use.
   if (empty($themes) || empty($modules)) {
     $themes = _system_rebuild_theme_data();
-    $modules = system_rebuild_module_data();
+    $modules = _system_rebuild_module_data();
   }
 
   if ($type == 'module' && isset($modules[$name])) {
@@ -1216,4 +1216,3 @@ function update_invoke_all() {
 
   return $return;
 }
-
Index: modules/system/system.admin.inc
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.admin.inc,v
retrieving revision 1.261
diff -u -p -r1.261 system.admin.inc
--- modules/system/system.admin.inc	6 Mar 2010 19:38:34 -0000	1.261
+++ modules/system/system.admin.inc	7 Mar 2010 01:24:54 -0000
@@ -373,8 +373,12 @@ function system_theme_enable() {
 
     // Check if the specified theme is one recognized by the system.
     if (!empty($themes[$theme])) {
-      theme_enable(array($theme));
-      drupal_set_message(t('The %theme theme has been enabled.', array('%theme' => $themes[$theme]->info['name'])));
+      $result = theme_enable(array($theme));
+      if (!$result) {
+        drupal_set_message(t('%theme could not be enabled.', array('%theme' => $themes[$theme]->info['name'])));
+      } else {
+        drupal_set_message(t('The %theme theme has been enabled.', array('%theme' => $themes[$theme]->info['name'])));
+      }
     }
     else {
       drupal_set_message(t('The %theme theme was not found.', array('%theme' => $theme)), 'error');
@@ -425,7 +429,13 @@ function system_theme_default() {
     if (!empty($themes[$theme])) {
       // Enable the theme if it is currently disabled.
       if (empty($themes[$theme]->status)) {
-       theme_enable(array($theme));
+       $result = theme_enable(array($theme));
+        if (!$result) {
+          //early return if we didn't actually enable a theme
+          drupal_set_message(t('%theme could not be enabled.', array('%theme' => $themes[$theme]->info['name'])));
+          drupal_goto('admin/appearance');
+          return;
+        }
       }
       // Set the default theme.
       variable_set('theme_default', $theme);
Index: modules/system/system.install
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.install,v
retrieving revision 1.452
diff -u -p -r1.452 system.install
--- modules/system/system.install	2 Mar 2010 09:09:45 -0000	1.452
+++ modules/system/system.install	7 Mar 2010 01:24:54 -0000
@@ -336,6 +336,22 @@ function system_requirements($phase) {
     }
   }
 
+  //See if we have any name conflicts between modules and themes
+  $requirements['name conflicts'] = array(
+    'title' => $t('Name Conflicts'),
+    'severity' => REQUIREMENT_OK,
+    'value' => $t('No conflicts'),
+  );
+  $themes = array_keys(_system_rebuild_theme_data());
+  $modules = array_keys(_system_rebuild_module_data());
+  $conflicts = array_intersect($themes, $modules);
+  if (count($conflicts)) {
+    $requirements['name conflicts']['severity'] = REQUIREMENT_ERROR;
+    $requirements['name conflicts']['value'] = $t('Conflicts: '). implode(', ', $conflicts);
+    $requirements['name conflicts']['description'] = $t('You may not have a module and a theme with the same name.');
+  }
+
+
   // Verify the update.php access setting
   if ($phase == 'runtime') {
     if (!empty($GLOBALS['update_free_access'])) {
@@ -1460,6 +1476,9 @@ function system_schema() {
       ),
     ),
     'primary key' => array('filename'),
+    'unique keys' => array(
+      'name' => array('name')
+      ),
     'indexes' => array(
       'bootstrap' => array('status', 'bootstrap', 'type', 'weight', 'name'),
       'system_list' => array('weight', 'name'),
@@ -2396,6 +2415,13 @@ function system_update_7050() {
 }
 
 /**
+ * Make {system}.name unique.
+ */
+function system_update_7051() {
+  db_add_unique_key('system', 'name', array('name'));
+}
+
+/**
  * @} End of "defgroup updates-6.x-to-7.x"
  * The next series of updates should start at 8000.
  */
Index: modules/system/system.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.module,v
retrieving revision 1.895
diff -u -p -r1.895 system.module
--- modules/system/system.module	3 Mar 2010 07:34:25 -0000	1.895
+++ modules/system/system.module	7 Mar 2010 01:24:55 -0000
@@ -2078,7 +2078,11 @@ function system_update_files_database(&$
       $file->schema_version = -1;
     }
   }
-  $query->execute();
+  try {
+    $query->execute();
+  } catch (Exception $e) {
+    drupal_set_message($e->getMessage(), 'error');
+  }
 }
 
 /**