Hmm,
i have here the following combo (with request monitor from head) running (aside of 6 other working combinations)
acs-kernel Kernel 5.3.2
xotcl-core XOTcl Core 0.56.2
xotcl-request-monitor XOTcl Request Monitor 0.39
xowiki xowiki 0.60.1
i have libthread 2.6.4, but afaik 2.6.1 should be ok.
XOTcl 1.5.3 should be fine as well
What base version of OpenACS are you using?
From which version did you upgrade?
Did you restart the server?
What is the first error message in the error.log?
