Office webapp doesn't work in owa

Hi all,

I have the following setup:

Exchangeserver 2013 Sp1

Office web app server SP1

When I try to open a attachment in Outlook i get te following message:

The translation:

The attachment in the browser must be viewed in the browser before downloading

If i klik on ok only the message disapears.

The settings seems right:

h t t p s://server/hosting/discovery is showing the right content

Officeserver:

FarmOU                            :
InternalURL                       : ******
ExternalURL                       : ********
AllowHTTP                         : False
SSLOffloaded                      : False
CertificateName                   : **********
EditingEnabled                    : True
LogLocation                       : C:\ProgramData\Microsoft\OfficeWebApps\Data\Logs\ULS
LogRetentionInDays                : 7
LogVerbosity                      :
Proxy                             :
CacheLocation                     : C:\ProgramData\Microsoft\OfficeWebApps\Working\d
MaxMemoryCacheSizeInMB            : 75
DocumentInfoCacheSize             : 5000
CacheSizeInGB                     : 15
ClipartEnabled                    : False
TranslationEnabled                : False
MaxTranslationCharacterCount      : 125000
TranslationServiceAppId           :
TranslationServiceAddress         :
RenderingLocalCacheLocation       : C:\ProgramData\Microsoft\OfficeWebApps\Working\waccache
RecycleActiveProcessCount         : 5
AllowCEIP                         : False
ExcelRequestDurationMax           : 300
ExcelSessionTimeout               : 450
ExcelWorkbookSizeMax              : 10
ExcelPrivateBytesMax              : -1
ExcelConnectionLifetime           : 1800
ExcelExternalDataCacheLifetime    : 300
ExcelAllowExternalData            : True
ExcelWarnOnDataRefresh            : True
OpenFromUrlEnabled                : False
OpenFromUncEnabled                : True
OpenFromUrlThrottlingEnabled      : True
PicturePasteDisabled              : True
RemovePersonalInformationFromLogs : False
AllowHttpSecureStoreConnections   : True
IgnoreDeserializationFilter       : False
Machines                          : {*********}

Exchange:

WacViewingOnPublicComputersEnabled     : True
WacViewingOnPrivateComputersEnabled    : True
ForceWacViewingFirstOnPublicComputers  : False
ForceWacViewingFirstOnPrivateComputers : False

Everything is as good as standard.

Thank you in advance!

Regards,

Fabian