We've upgraded our installation and that overall did not go very smooth. After manual upgrade steps, we got it working, but we now have one issue in the web interface, and that is that when the interface loads, an error pops up:

Details of the error are:

An error occurred while initializing the zimlet "com_zimbra_attachcontacts". Please notify administrator.
TypeError: this.handlerObject._init is not a function

At first, this started happening for WebEx zimlet. I disabled it, and then there was an error with srchhighlighter zimlet. I disabled that one, and the error is now with attachcontacts zimlet. And so on.. I disabled linkedin, attachcontacts and zimbra social. Now the problem has gone away, but those zimlets are disabled.

Is this a zimlet issue or maybe a general one, but the zimlets which have been left enabled just don't use some functionality which would trigger the above error?

I don't really know where to look; the log files show no errors. We also have a staging environment with 7.0.1GA where there are no problems and zimlets are working fine (that system has been upgraded a week or so ago).

What to check next, where to look?