Error in initFields(scales = scales) : could not find function "initRefFields" - r

Question

I have a ggplot2 plotting function as part of my code.
The function works fine when the file is sourced as R code, however when I include this function in an R package (and of course I include ggplot2 and scales both in the DESCRIPTION and in the NAMESPACE files of the package) I am getting the following error:
Error in initFields(scales = scales) :
could not find function "initRefFields"
The respective call of scales in the ggplot2 object is the following:
+ facet_wrap(~PV_Type, ncol = 1, scales = "free") +
I run the latest R (3.2.0) and the latest ggplot2 (1.0.1) installed from source.
A possible solution/explanation will be highly appreciated!
EDIT: The output of sessionInfo() is the following:
R version 3.2.0 (2015-04-16)
Platform: x86_64-apple-darwin13.4.0 (64-bit)
Running under: OS X 10.10.3 (Yosemite)
locale:
[1] C/UTF-8/C/C/C/C
attached base packages:
[1] stats graphics grDevices utils datasets base
other attached packages:
[1] argparse_1.0.1 proto_0.3-10 greater_1.0
loaded via a namespace (and not attached):
[1] Rcpp_0.11.6 DEoptimR_1.0-2 RColorBrewer_1.1-2 plyr_1.8.2
[5] methods_3.2.0 class_7.3-12 prabclus_2.2-6 tools_3.2.0
[9] digest_0.6.8 mclust_5.0.1 gtable_0.1.2 lattice_0.20-31
[13] mvtnorm_1.0-2 findpython_1.0.1 gridExtra_0.9.1 trimcluster_0.1-2
[17] stringr_1.0.0 cluster_2.0.1 RGraphics_2.0-12 fpc_2.1-9
[21] stats4_3.2.0 diptest_0.75-6 grid_3.2.0 nnet_7.3-9
[25] getopt_1.20.0 robustbase_0.92-3 flexmix_2.3-13 pander_0.5.1
[29] ggplot2_1.0.1 reshape2_1.4.1 kernlab_0.9-20 magrittr_1.5
[33] scales_0.2.4 modeltools_0.2-21 MASS_7.3-40 colorspace_1.2-6
[37] stringi_0.4-1 munsell_0.4.2 rjson_0.2.15
The .libPaths() is also rather common for my installation:
>.libPaths()
[1] "/Library/Frameworks/R.framework/Versions/3.2/Resources/library"
Perhaps I should also add that I call the function which requires the scales package from a command line R script.
(This is not a duplicate of ggplot2 Error in initFields as I tried all their recommendations (apart from reverting back to R 2.14 of course) and none worked).

Answer 1

I think I have found a solution/workaround.
As I noticed from sessionInfo() the methods package was not attached but rather loaded in the namespace. Therefore after attaching methods (as well as grid which was needed for a consequent function) my script work fine by oading the functions from the package.
My working sessionInfo() looks like this now:
R version 3.2.0 (2015-04-16)
Platform: x86_64-apple-darwin13.4.0 (64-bit)
Running under: OS X 10.10.3 (Yosemite)
locale:
[1] C/UTF-8/C/C/C/C
attached base packages:
[1] grid methods stats graphics grDevices utils datasets
[8] base
other attached packages:
[1] argparse_1.0.1 proto_0.3-10 greater_1.0
loaded via a namespace (and not attached):
[1] Rcpp_0.11.6 DEoptimR_1.0-2 RColorBrewer_1.1-2 plyr_1.8.2
[5] class_7.3-12 prabclus_2.2-6 tools_3.2.0 digest_0.6.8
[9] mclust_5.0.1 gtable_0.1.2 lattice_0.20-31 mvtnorm_1.0-2
[13] findpython_1.0.1 gridExtra_0.9.1 trimcluster_0.1-2 stringr_1.0.0
[17] cluster_2.0.1 RGraphics_2.0-12 fpc_2.1-9 stats4_3.2.0
[21] diptest_0.75-6 nnet_7.3-9 getopt_1.20.0 robustbase_0.92-3
[25] flexmix_2.3-13 pander_0.5.1 ggplot2_1.0.1 reshape2_1.4.1
[29] kernlab_0.9-20 magrittr_1.5 scales_0.2.4 modeltools_0.2-21
[33] MASS_7.3-40 colorspace_1.2-6 stringi_0.4-1 munsell_0.4.2
[37] rjson_0.2.15
Thanks very much for the contribution, however I would appreciate an explanation on firstly why there is the need to explicitly attach these two packages (methods and grid) when the functions are loaded as a package, and it is not required when the function are sourced by source().