Hey there,

a production site suddenly started acting up, where new documents can no longer be published. The log shows the following error:

SEOChecker: Error during validating tag for document: 2441 using validator 'BrokenLinks'
System.ArgumentNullException: Value cannot be null.
Parameter name: format
   at System.String.FormatHelper(IFormatProvider provider, String format, ParamsArray args)
   at SEOChecker.Validators.ContentValidators.Links.BrokenLinkValidator.Parse(ValidationResult result, IUmbracoDocument document, HtmlDocument htmlDocument, IContextInfo contextInfo)
   at SEOChecker.Core.Validation.SEOValidator.Validate(ValidationResult validationResult, IUmbracoDocument document, HtmlDocument htmlDocument, IContextInfo context)

Strange thing is that this message comes after the following line:

Content 'test123' with Id '2441' has been published.

Umbraco saves all changes just fine, but it seems before actually publishing, this error pops up and it also prevents re-creating the umbraco.config file.

I've connected my local environment to the production database and tried attaching a debugger but when I try that no errors appear and everything works as it should (and subsequently, my umbraco.config is updated).

It's an Umbraco 7.2.5 site, SEOChecker 1.9.3, hosted in an Azure Webapp. There have been no changes to the code with the exception from CMS (content) changes for over a week.

Currently I'm at a loss on what causes this error. Any help is appreciated.

Thanks,

DJ