Error during Massupdate and setting Show Datasets per Page too high

[CeWa]

I did a massupdate on accounts (889 entries) to change assigned users. It worked but threw out an 403 error:

(
    [controller] => Account
)
, InputData:  -  [] []
[2014-11-24 13:45:33] Espo.ERROR: Display Error: , Code: 403 URL: /espocrm/api/v1/Account?maxSize=889&offset=0&sortBy=name&asc=true&where%5B0%5D%5Btype%5D=equals&where%5B0%5D%5Bfield%5D=assignedUserId&where%5B0%5D%5Bvalue%5D=1 [] []
[2014-11-24 13:49:25] Espo.ERROR: API [GET]:/:controller, Params:Array

Also, same error when setting Shows Datasets per page to say, 400:

(
    [controller] => Account
)
, InputData:  -  [] []
[2014-11-24 13:51:17] Espo.ERROR: Display Error: , Code: 403 URL: /espocrm/api/v1/Account?maxSize=400&offset=0&sortBy=name&asc=true [] []
[2014-11-24 13:51:29] Espo.ERROR: API [GET]:/:controller, Params:Array