This content type has inactive fields...

I'm not familiar with this message. I'm assuming it's coming from CCK. Are you able to temporarily switch the field to just a basic "select" widget for testing purposes to see if the error message goes away?

You should be able to temporarily change the widget for your field. Go to Content Management > Content Types > Edit [YOUR CONTENT TYPE] > Manage Fields > [YOUR FIELD] > Change basic information > Widget type: Select list.

Then try to create a new node of this type and see if you're getting the same issue. If you're still seeing it, that means it's not being caused by something related to Multiselect. If you aren't seeing it after the change, then we'll need to investigate further.

I have the same problem.
The multiselect field doesnot appear in the nodetype filed manager.
How to active it?
If you can solve this, plz tell me.Thx.

I strongly recommend making a backup of your database before you try this.

You can try manually changing the field type directly inside the database with the following commands. Be sure to replace [YOUR-FIELD-HERE] inside the command.

UPDATE `content_node_field_instance` SET `widget_type` = 'optionwidgets_select',
`widget_module` = 'optionwidgets' WHERE `field_name` = 'field_[YOUR-FIELD-HERE]';
TRUNCATE `cache`;

This should change it temporarily to a normal CCK select list hopefully.

Just to note, you don't really have to run update.php all those times.

It should be sufficient to change the widget in your database, and then re-install the CCK modules (You can use Devel to do that.)

In case it's of help to anyone else... I had the same problem here except that the module for the given widget was actually installed. In that case, just changing the widget_active column on its table row did the trick—no need to change the widget type at all. So, in the form of an SQL query based on the above (#6), it would be as follows:

UPDATE `content_node_field_instance` SET `widget_active ` = 1 WHERE `field_name` = 'field_[YOUR-FIELD-HERE]';
TRUNCATE `cache`;

I just upgraded from D5 and used the latest 6.x-1.7 version of this module. Using the latest CCK 6.x-2.9.

Multiselect fields didn't show up in my nodes and they were missing from the 'manage fields' view of content type administration, too.

Reason

• The reason for this behavior is the same as suggested in comment #6:
• the column 'widget_active' was left to value '0' in the {content_node_field_instance} database table.

Workaround / fix

• Manually updating these values to '1' for all records where the widget_type is 'multiselect_select' fixed the problem.
• Remember to clear cache after this (using e.g. devel module or the button on admin/settings/performance)

Fix for root cause
It would be useful if someone could investigate the root cause of why 'widget_active' is left '0' during the upgrade. I don't have experience on implementing widgets to CCK so unfortunately I can't help on this but I hope that the information above helps in this.

Edit:
Added the clear cache step to the workaround.

http://drupal.org/node/500360#comment-3966954 enabled my old d5 text field at first.

Still, /edit and /devel were giving empty values, so useless.

Since I prefer not to touch Drupal DB schema , I went for a different approach:

.create a brand new field with same attributes (example: fieldname_d6)
.copy values from old column to new column by SQL :
update content_type_quartiere set field_new_d6_field_value = field_old_d5_field_value ;

After which, I had same old values from Drupal 5 inside a brand new D6 cck field.
If your custom code needs thosevalues, you'll have to correct SQL in your module code with new field name, of course.