I am having trouble accessing and editing in the CMS admin, I get these errors sometimes but not all the time! It has problems accessing the admin and also saving changes please could someone advise me as to what this means:

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ERROR [User Error]: Couldn't run query:
SHOW FULL FIELDS IN `Permission`

Got error 28 from storage engine
IN POST /admin/getitem?ID=5&ajax=1
Line 401 in /home/sites/mysite.co.uk/public_html/sapphire/core/model/MySQLDatabase.php

Source
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392:    }
393:    
394:    function databaseError($msg, $errorLevel = E_USER_ERROR) {
395:       // try to extract and format query
396:       if(preg_match('/Couldn\'t run query: ([^\|]*)\|\s*(.*)/', $msg, $matches)) {
397:          $formatter = new SQLFormatter();
398:          $msg = "Couldn't run query: \n" . $formatter->formatPlain($matches[1]) . "\n\n" . $matches[2];
399:       }
400:       
* 401:       user_error($msg, $errorLevel);
402:    }
403: }
404:
405: /**
406: * A result-set from a MySQL database.
407: * @package sapphire

<ul>user_error(Couldn't run query:
SHOW FULL FIELDS IN `Permission`

Got error 28 from storage engine,256)
line 401 of MySQLDatabase.php

MySQLDatabase->databaseError(Couldn't run query: SHOW FULL FIELDS IN `Permission` | Got error 28 from storage engine,256)
line 102 of MySQLDatabase.php

MySQLDatabase->query(SHOW FULL FIELDS IN `Permission`,256)
line 120 of DB.php

DB::query(SHOW FULL FIELDS IN `Permission`)
line 276 of MySQLDatabase.php

MySQLDatabase->fieldList(Permission)
line 271 of DB.php

DB::fieldList(Permission)
line 942 of Security.php

Security::database_is_ready()
line 84 of Controller.php

Controller->init()
line 100 of LeftAndMain.php

LeftAndMain->init()
line 84 of CMSMain.php

CMSMain->init()
line 113 of Controller.php

Controller->handleRequest(HTTPRequest)
line 277 of Director.php

Director::handleRequest(HTTPRequest,Session)
line 121 of Director.php

Director::direct(/admin/getitem)
line 118 of main.php

</ul>