Solving "Unexpected Store Error" in Exchange

Getting a weird COM Exception with the cryptic ID 0x8055001E?

We’ve been struggling with this problem for over a year now, and we finally have a solution.

We have some critical code that is contacting Exchange server via COM Interop and CDOEX.DLL to read some inboxes and process e-mails. About once a month or so, we get this error:

System.Runtime.InteropServices.COMException (0x8055001E): Unexpected
store error: %1!d! (0x%1!8.8x!)
   at ADODB.RecordsetClass.Open(Object Source, Object
ActiveConnection, CursorTypeEnum CursorType, LockTypeEnum LockType,
Int32 Options)
   at MessageService.Exchange.ExchangeClient.Connect(String folderUrl,
String userId, String password, Boolean useHttp)

After this point, restarting our software does not help. The only recourse is to restart the Exchange store completely. Did I mention that our software needs to run 24/7/365 with no downtime (a few minutes here and there are acceptable)?

So about once a month, I get a message on my phone, I log into the server, reboot Exchange, and all is well.

Searching on Google revealed nothing at all. Until recently.

I now believe the problem was we were checking two e-mail accounts back-to-back, in a loop like this (highly simplified):

while (running)

Apparently, there is some bug in the CDO COM components’ code that will cause errors if you reconnect too fast. Occasionally, the Exchange code must have completed so quickly that it didn’t provide enough time for the COM components to clean up properly before the next solution attempt. Solution?

while (running)

We implemented that change on a staging server that was also experiencing this problem and haven’t had a single reoccurrence since. The fix will be going into production very soon. No more 2AM alerts!

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