TYPO3 6.2: "Could not find a suitable type converter for "String" " exeption after update

Question

TYPO3 was from a very old version updated to TYPO3 6.2. The most things are working now, but I have one own written extension that give me the following error:

Core: Exception handler (WEB): Uncaught TYPO3 Exception: #1297759968: Exception while property mapping at property path "":Could not find a suitable type converter for "String" because no such class or interface exists. | TYPO3\CMS\Extbase\Property\Exception thrown in file /srv/vhosts.d/typo3_src-6.2.9/typo3/sysext/extbase/Classes/Property/PropertyMapper.php in line 106.

I have a list Method in one of the controller that generates a link:

<f:link.action action="show" arguments="{id : course.id}"> {course.name}</f:link.action>

This list method works, but when I want to open this generated link in the website I get the error from above.

I delete all stuff in the showAction method and also change the template to a basic output without special things. The method looks than like this:

 /**
 * action show
 *
 * @param String Course-Id
 * @return void
 */
public function showAction($id){

}

But the error is still there. I have absolutely no idea anymore what is the problem. It would be great when someone have a different view and properly have some ideas where I can try to find out what the problem really is.

Answer 1

I think it needs to be

 /**
  * action show
  *
  * @param string $id Course-Id
  * @return void
  */
 public function showAction($id){

 }

string lowercase and the argument $id must be specified as well

Answer 2

I want to share my solution way:

The first problem was that I don't know that there is a new way to delete the cache of the core. That I find out because of Jost comment in my answer with the "clear the cache from install tool". So I go in the Backend of Typo3 to edit a user and edit there my own under Options the TSconfig field. I add there a row with options.clearCache.system = 1. Now I can clear the system core over the flash symbol in the Backend of Typo3.

After that I try to change the @param String in @param string. I deleted the core cache and then I got a different error. I found out that this new error say that only arrays or objects are as parameters are allowed in the action method (See: http://wiki.typo3.org/Exception/CMS/1253175643). So I deleted the parameter and follow the instruction on the website where the error is explained. So my new method looks as follow:

/**
* action show
*
* @return void
*/
public function showAction(){
    if ($this->request->hasArgument('id')) {
        $id= $this->request->getArgument('id');
    }
    // Do stuff with the id
}

And that works now :)