Few people remember all the parameters of FOPEN, so here they are:

Text version.

filenum:=FOPEN(filename	{array of 36 bytes}
,foptions	{logical value, file options}
,aoptions	{logical value, access options}
,recsize	{integer value,+=words,-=bytes}
,device	{array of 8 bytes}
,formsmsg	{array of bytes}
,userlabels	{integer value, 0 to 255}
,blockfactor	{integer value, 1 to 255}
,numbuffers	{integer value, 0 to 16}
,filesize	{double value, maximum records}
,numextents	{integer value, 1 to 32}
,initalloc	{integer value, starting extents}
,filecode	{integer value, file type code}
);	{option variable}

If FOPEN fails, filenum will be 0 and you call FCHECK to get the error number. Check the filenum for errors, not the Condition code, which has a lamentable tendency to change before you check it. Certain errors are common and should be anticipated in your program: no such account (50), no such group (51), no such file (52), no such TEMP file (53), invalid filename format (54), no $oldpass (58), can't give exclusive access (90), someone has exclusive access (91), wrong lockword (92), security violation (93), you didn't specify the same lock/nolock option as other users did (48).