[imp] link attachment's url doesn't work

[Jean Charles Delépine]

Hello,

The url given in mail while sending a big file via imp :

1. rmc-20090924.ogg (99,8 Mo) [audio/ogg]
Télécharger le lien :
https://webmail.u-picardie.fr/services/ajax.php/horde/imp/attachment.php?id=5644adc9-9294-48b5-836f-73e90a008464&u=delepine

doesn't work : here's what firefox give me :
/*-secure-{"msgs":[{"message":"\/services\/ajax.php\/horde\/login.php?url=%2Fservices%2Fajax.php%2Fhorde%2F&horde_logout_token=vCeYcIzkd732-VlAfQbr7RI&logout_reason=6","type":"horde.ajaxtimeout"}],"response":false}*/

while this url works fine :
https://webmail.u-picardie.fr/imp/attachment.php?id=5644adc9-9294-48b5-836f-73e90a008464&u=delepine

I can't find any error in logs.

Horde Groupware Webmail Edition 5.2.11, imp 6.2.11.

I didn't find any answer in the list archive.