Warning in .make_numeric_version(x, strict, .standard_regexps()$valid_numeric_version) :
  invalid non-character version specification 'x' (type: double)
Calls:
 1: tools:::.load_namespace_rather_quietly("opencpu")
 2: withCallingHandlers(suppressMessages(eval(expr)), warning = .whandler)
 3: suppressMessages(eval(expr))
 4: withCallingHandlers(expr, message = function(c) if (inherits(c, classes)) tryInvokeRestart("muffleMessage"))
 5: eval(expr)
 6: eval(expr)
 7: loadNamespace("opencpu")
 8: runHook(".onLoad", env, package.lib, package)
 9: tryCatch(fun(libname, pkgname), error = identity)
10: tryCatchList(expr, classes, parentenv, handlers)
11: tryCatchOne(expr, names, parentenv, handlers[[1L]])
12: doTryCatch(return(expr), name, parentenv, handler)
13: fun(libname, pkgname)
14: ocpu_init()
15: create_user_config()
16: get_user_conf()
17: file.path(getlocaldir("config"), "user.conf")
18: getlocaldir("config")
19: Ops.numeric_version(getRversion(), 4)
20: as.numeric_version(e2)
21: numeric_version(x)
22: .make_numeric_version(x, strict, .standard_regexps()$valid_numeric_ve [... truncated]
Warning in .make_numeric_version(x, strict, .standard_regexps()$valid_numeric_version) :
  invalid non-character version specification 'x' (type: double)
Calls:
 1: tools:::.load_namespace_rather_quietly("opencpu")
 2: withCallingHandlers(suppressMessages(eval(expr)), warning = .whandler)
 3: suppressMessages(eval(expr))
 4: withCallingHandlers(expr, message = function(c) if (inherits(c, classes)) tryInvokeRestart("muffleMessage"))
 5: eval(expr)
 6: eval(expr)
 7: loadNamespace("opencpu")
 8: runHook(".onLoad", env, package.lib, package)
 9: tryCatch(fun(libname, pkgname), error = identity)
10: tryCatchList(expr, classes, parentenv, handlers)
11: tryCatchOne(expr, names, parentenv, handlers[[1L]])
12: doTryCatch(return(expr), name, parentenv, handler)
13: fun(libname, pkgname)
14: ocpu_init()
15: load_config_and_settings(preload = TRUE)
16: get_user_conf()
17: file.path(getlocaldir("config"), "user.conf")
18: getlocaldir("config")
19: Ops.numeric_version(getRversion(), 4)
20: as.numeric_version(e2)
21: numeric_version(x)
22: .make_numeric_version(x, strict, .standard_regexp [... truncated]

A namespace must be able to be loaded with just the base namespace
loaded: otherwise if the namespace gets loaded by a saved object, the
session will be unable to start.

Probably some imports need to be declared in the NAMESPACE file.