[horde] Could not pack data

[Per olof Ljungmark]

Need a clue to why I get this at the login prompt in a new testing
install for 5.2.1.

HORDE: Could not pack data. [pid 23141 on line 154 of
"/usr/local/share/pear/Horde/Pack.php"]

No other info is logged, just this. AFAICS everything required is there.

The test.php script is fine for horde and imp. but ingo, kronolith and
turba test pages also throws "Could not pack data."

Any hints greatly appriciated.