An admin user cannot perform context.ExecuteQuery()

In the company we are running multiple scripts against multiple SharePoint Online tenants. They all involve context.ExecuteQuery() at some point. No-one has any issues apart from one user on one specific computer.

If I use my credentials on his computer - it works. So it's not a system issue/dependencies/configuration.

If he uses his credentials on my computer - it works. So it's not a credential issue/permission/access.

When he uses his credentials on his computer - the app crashes/doesn't run, depending on error handling. The issue appears with both Powershell scripts and C# solutions. Error from one of the apps:

Unhandled Exception: System.ArgumentException: '.', hexadecimal value 0x00, is a

n invalid character.

at System.Xml.XmlEncodedRawTextWriter.InvalidXmlChar(Int32 ch, Char* pDst, Bo

olean entitize)

at System.Xml.XmlEncodedRawTextWriter.WriteElementTextBlock(Char* pSrc, Char*

pSrcEnd)

at System.Xml.XmlEncodedRawTextWriter.WriteString(String text)

at System.Xml.XmlWellFormedWriter.WriteString(String text)

at System.Xml.XmlWriter.WriteElementString(String localName, String ns, Strin

g value)

at Microsoft.SharePoint.Client.Idcrl.IdcrlUtility.XmlValueEncode(String value

)

at Microsoft.SharePoint.Client.Idcrl.IdcrlAuth.BuildWsSecurityUsingUsernamePa

ssword(String username, String password)

at Microsoft.SharePoint.Client.Idcrl.IdcrlAuth.GetServiceToken(String usernam

e, String password, String serviceTarget, String servicePolicy)

at Microsoft.SharePoint.Client.Idcrl.SharePointOnlineAuthenticationProvider.G

etAuthenticationCookie(Uri url, String username, SecureString password)

at Microsoft.SharePoint.Client.SharePointOnlineCredentials.GetAuthenticationC

ookie(Uri url, Boolean refresh)

at Microsoft.SharePoint.Client.ClientRuntimeContext.SetupRequestCredential(Cl

ientRuntimeContext context, HttpWebRequest request)

at Microsoft.SharePoint.Client.SPWebRequestExecutor.GetRequestStream()

at Microsoft.SharePoint.Client.ClientContext.GetFormDigestInfoPrivate()

at Microsoft.SharePoint.Client.ClientContext.EnsureFormDigest()

at Microsoft.SharePoint.Client.ClientContext.ExecuteQuery()

at CreateLists.Program.CreateAnnouncementsList(String site, String credUserna

me, SecureString password, Int32 itemsno)

at CreateLists.Program.Main(String[] args)

I suspected his credentials were somehow cached on his computer so we:

* cleared the cache

* flushed the dns

* cleared all credentials from the credentials manager

* there is no DirSync or Federation on the tenant

* there are no issues on other computers in this network



The issue still persists.