[Tex/LaTex] bibliography/citing error every other time, no in-text citations

Question

To prepare submission for a journal, I am practically forced to use the sagej documentclass, available here: SAGE. My MWE looks like this:

\documentclass[PCfour,sageh,times,doublespace]{sagej}
% add doublespace for submitting for review
\usepackage{moreverb,url}

%\input{preambleOS}
\usepackage[colorlinks,bookmarksopen,bookmarksnumbered,citecolor=red,urlcolor=red]{hyperref}

\begin{document}
cite like this: \cite{R1} and \citep{R2} and \citet{R2}

but why not like this like this: \cite{Fama1992} and \citep{Fama1992} and \citet{Fama1992}

\begin{thebibliography}{99}
\bibitem[Kopka and Daly(2003)]{R1}
Kopka~H and Daly~PW (2003) \textit{A Guide to \LaTeX}, 4th~edn.
Addison-Wesley.

\bibitem[Lamport(1994)]{R2}
Lamport~L (1994) \textit{\LaTeX: a Document Preparation System},
2nd~edn. Addison-Wesley.
\end{thebibliography}

\bibliography{mwebiblio}
\bibliographystyle{mslapa}

\end{document}

The style mslapa is suggested by the journal, and described as a very generic default style:

"Please note that the files SageH.bst and SageV.bst are included with
the class file for those authors using BIBTEX. For APA style references
please use mslapa.bst which should be part of most modern TEX
distributions. See the above instructions regarding choos- ing the
correct reference option."

The bibliography file mwebiblio contains this (when opened in Texworks; I use Texworks and Miktex):

% Encoding: windows-1252

@Article{Fama1992,
  author  = {Eugene F. Fama and Kenneth R. French},
  title   = {The Cross-Section of Expected Stock Returns},
  journal = {The Journal of Finance},
  year    = {1992},
  volume  = {47},
  number  = {2},
  pages   = {427-465},
}

@Comment{jabref-meta: databaseType:bibtex;}

When I compile, after having manually deleted all aux, bbl, and other files, it compiles (pdfLaTeX) great once, but the second time, I receive the error:

! Missing = inserted for \ifnum.
<to be read again> 
                   \def 
l.14 ...y not like this like this: \cite{Fama1992}
                                                   and \citep{Fama1992} and ...

From then on, the next compiling will go through without error, then this error again, etc.

However, the output is never satisfactory, because the in-text citations relating to the bib-file are always only question marks:

What I need is to include an external bibliography file (created with Jabref) with working in-text citations, as in the first sentence in the picture. (The only reason why I include the two entries manually and the bib-file at the same time here is to demonstrate the problem.)

---

What I played with is to replace sageh with sageapa in the class options, because I actually want to cite in APA style. But then I obtain the error:

! Undefined control sequence.
l.14 ...this like this: \cite{Fama1992} and \citep
                                                  {Fama1992} and \citet{Fama...

for seemingly every citing command that is not just plain cite. I noticed that the combination of sageh and \bibliographystyle{mslapa} is also in accordance with APA, so me having to use sageh like this is no further problem, but perhaps relevant to the first problem and its solution.

Answer 1

If you want to use the mslapa style then you must load the class with the sageapa option -- this will load the mslapa.sty instead of natbib (which is not compatible with the bst). You then can't use \citep and \citet:

\documentclass[PCfour,sageapa,times,doublespace]{sagej}
% add doublespace for submitting for review
\usepackage{moreverb,url}

%\input{preambleOS}
\usepackage[colorlinks,bookmarksopen,bookmarksnumbered,citecolor=red,urlcolor=red]{hyperref}

\begin{document}

 but why not like this like this: \cite{Fama1992} and 


\bibliography{test}
\bibliographystyle{mslapa}

\end{document}