I'd like to step in here ---- We experience a similar problem, even worse.
This relates to D365 for Finance and Operations, Enterprise edition (D365FFOEE, aka "AX7"); platform update 12 as of 2017/November.
We set up a new on-premise development environment based on VM ("Dev") downloaded from MS Connect for Dev/Test/Demo on premise.
Added our custom code packages, did a full build and DB sync -- everything fine.
Starting the client in the browser I am able to log in without problems, DefaultDashboard loads, the common "start screen" of D365FFOEE appears but after 2 seconds I get just the same error message "An unexpected client error has occured". Click on Close --> message disappears but from now on the UI becomes nearly unresponsive: click on any tile of dashboard or click on options gear icon --> nothing happens. The first level of the main menu is the only thing I can reach, second level is unreachable.
Has anyone experienced this or a similar problem with that release of D365FFOEE?
I have tried nearly everything that an average developer should try in such situation: Refresh, empty cache, use other browser, use browser on server or on remote client, restart IIS, modified some properties of IIS application pool and site settings, reboot machine, rebuild code, ... etc.
Nothing helped, always the same error pops up.
I looked into Event Log (on the general Application level): no related event message. Looked into several of those round about 50 AX-related specific logs in Event Viewer: all are empty (same as Jan M. observed...)
Similar to what Jan M. reports: we had this error once in a while (veeeery unfrequently) in an older release (PU7). However the error then never occured immediately after start screen loading but rather while working in forms etc. We clicked 'Close', message disappeared an everything continued normal. No unresponsive UI etc. But now the problem is different and severe.
Any suggestions?
Any idea where else I could look to find the error cause.
Many thanks in advance,
-- Sven