Thunderbird/Lightning calendar error: no detail, no way to correct

[oxy]

Hi,

since a while my home calendar (lightning) is giving periodically
an error popup window like:

    "An error occured when writing to the calender Home!"

I click on "Detail" and get:

    "error code: MODIFICATION_FAILED"
    "Description:" (empty)


This is the same as no information for me.
How can i correct that?
The calendar is sync to google with the addon "provider for google
calendar". (v0.25)

Thbird 24.3.0
Lightning 2.6.3
Ubuntu 12.04

thx for any help!

PS: cross post with https://forums.mozilla.org/addons/viewtopic.php?f=23&t=16525
No answer there.